21 Days Theory – Series Review & Ending Explained

21 Days Theory is a Thai BL series about a high school relationship developed over three weeks.

21 Days Theory is a Thai BL series about a high school romance that develops over three weeks. The main character meets a cheeky older student who challenges him to an unconventional competition. He must convince a famous girl to take him on a date over the next twenty-one days. Although their relationship begins as a rivalry, the two leads become closer as they get to know each other better.

Even though it falls into the category of BL fluff, I enjoy watching 21 Days Theory. This adorable love story compensates for its flimsy plot with lots of buoyant humour and delightful charm. The two endearing leads carry their sweet teen romance with a fun, easygoing vibe. It's an above-average series that wraps up satisfyingly in four compact episodes.

21 Days Theory Summary


21 วัน มีฉันมีเธอ

Series Info:

Thailand (2022)


3 hours

Total Episodes:

4 episodes


School romance


21 Days Theory is a cute & sweet BL drama.


Q and X are high school students who flirt with each other.

Q is a high school student who lives with his mom and uncle. Their family runs a bakery business from home. His mother wants to promote a business by seeking a review from Mook, an online celebrity who goes to the same school as her son. Mook is the school's representative for Ship for Southeast Asian & Japanese Youth Program (SSEAYP), a famous student exchange program. However, Q and Mook don't know each other. His family reluctantly gives up on the marketing idea.

Q's mother wants her handsome son to pursue an acting career. She encourages him to attend acting auditions, although Q has never secured a role successfully. One day, he goes to another casting call. Q meets X, a senior student who goes to the same school as him. X is also a representative of SSEAYP. Since both are competing for the same acting gig, the cheeky X teases Q and plays mind games on his opponent. As a result, Q becomes flustered and feels irritated around X.

After the audition, Q's friend Toy changes his mind about giving him a ride home. Q reluctantly hitches a ride with X instead. They arrive at Q's home. Then, X boldly introduces himself to Q's family, who invite him to have dinner together. X is polite and charming during the meal, making an excellent first impression. He even helps the mom communicate with an English-speaking customer. Nonetheless, Q remains annoyed because this manipulative stranger won't leave him alone.

As X prepares to leave home for the night, he offers an unusual proposal. X challenges Q to a quirky competition. In the next 21 days, Q must find a way to become Mook's date at an upcoming SSEAYP awards ceremony. If he succeeds, X will grant him any wish he wants. Otherwise, Q must reciprocate the favour. It isn't easy, considering Q has no relationship with the famous Mook. Nevertheless, his competitive streak kicks in, and he accepts the quirky deal.

The competition unfolds over the next three weeks. Q plots with his friends Toy and Frank each day, devising plans to get closer to Mook. They adopt a secret admirer identity and leave anonymous gifts in Mook's classroom. Meanwhile, X finds opportunities to chat with Q, checking on his progress. The two rivals don't get along initially, but their hostility subsides. They go from antagonizing each other to spending much time together.

21 Days Theory Cast



Tee Khunakorn Sunantham (ตี๋ คุณากร สุนันธรรม)

Q is portrayed by the Thai actor Tee Khunakorn Sunantham (ตี๋ คุณากร สุนันธรรม).

Q is a high school student who lives with his mom and uncle. Their family runs a bakery business from home. Q is an aspiring actor and attends regular auditions, although he never succeeds in securing a role. Q is best friends with Toy and Frank at school.

Tee Khunakorn Sunantham

Tee Khunakorn Sunantham (ตี๋ คุณากร สุนันธรรม) is a Thai actor. He is born on October 8, 2000.

Tee Khunakorn Sunantham (ตี๋ คุณากร สุนันธรรม) is a Thai actor. He is born on October 8, 2000. His first BL project is the 2021 series, The Cupid Coach. He also stars in the 2022 drama, 21 Days Theory.


Bever Patsapon Jansuppakitkun (บีเวอร์ พรรษพล เจนสรรพกิจกุล)

X is portrayed by the Thai actor Bever Patsapon Jansuppakitkun (บีเวอร์ พรรษพล เจนสรรพกิจกุล).

X is a senior student who goes to the same school as Q. They meet in an acting audition, where a friendly rivalry develops between the two teens. Q used to live overseas and attended a boarding school, but he's settling in Thailand for his final year. Q and his friend Mook are the school's representatives for the Ship for Southeast Asian & Japanese Youth Program (SSEAYP).

Bever Patsapon Jansuppakitkun

Bever Patsapon Jansuppakitkun (บีเวอร์ พรรษพล เจนสรรพกิจกุล) is a Thai actor. He is born on September 7, 1998.

Bever Patsapon Jansuppakitkun (บีเวอร์ พรรษพล เจนสรรพกิจกุล) is a Thai actor. He is born on September 7, 1998. His first BL project is a supporting role in the 2020 franchise, En of Love. He also appears in The Best Story (2021) and Love Mechanics (2022). Bever's first leading role is in the 2022 drama, 21 Days Theory.

Supporting Cast

Toy is portrayed by the Thai actor Prat Itthichaicharoen (ปรัชญ์ อิทธิชัยเจริญ).


Prat Itthichaicharoen (ปรัชญ์ อิทธิชัยเจริญ)

Frank is portrayed by the Thai actor Bigboom Jirayu Sahguansin (บิ๊กบูม จิรายุ สงวนศิลป์).


Bigboom Jirayu Sahguansin (บิ๊กบูม จิรายุ สงวนศิลป์)

Mook is portrayed by the Thai actress Bambam Pischapron Ketawattananon (พิชชาพร คีตวัฒนานนท์).


Bambam Pischapron Ketawattananon (พิชชาพร คีตวัฒนานนท์)

Mind is portrayed by the Thai actress Bell Warisara Jitpreedasakul (วริศรา จิตปรีดาสกุล).


Bell Warisara Jitpreedasakul (วริศรา จิตปรีดาสกุล)

Q's mom is portrayed by the Thai actress Maneenun Ningsanond.

Q's mom

Maneenun Ningsanond

Man is portrayed by the Thai actor Sarawut Siriphet (ศราวุธ ศิริเพชร).


Sarawut Siriphet (ศราวุธ ศิริเพชร)

The principal is portrayed by the Thai actor Aphiwit Warathum.


Aphiwit Warathum

Cast Highlights

  • Q's actor (Tee) is the star of the 2021 Thai fantasy BL series The Cupid Coach.
  • The actor who portrays X (Bever) appeared in various supporting roles. His portfolio of work include En of Love: Love Mechanics (2020), The Best Story (2021), and Love Mechanics (2022).
  • Toy and Frank's actors (Prat and Bigboom) both appeared in Love Mechanics. Bigboom is the star of the 2023 BL series Future. In addition, Prat also had supporting roles in the En of Love franchise and The Best Story.

21 Days Theory Review


Drama Review Score: 7.6

X sneaks up on Q unexpectedly.

21 Days Theory is a super cute BL drama, even though the series begins with a flimsy premise. The so-called competition doesn't make much sense. I've no idea why the protagonist would agree to a vague and pointless rivalry. However, the strange scenario is a MacGuffin, establishing a convenient excuse for the two leads to interact with each other. Rather than questioning the plot, it's easier to simply enjoy the funny and lighthearted journey. 21 Days Theory compensates for a shaky story with humour, enthusiasm & charm.

The first episode is slightly clunky, introducing the central storyline with a heavy hand. As the plot unfolds, the events and interactions feel contrived. Also, X's character makes a lousy first impression. His early behaviour comes across as conniving and antagonistic. I keep waiting for him to apologize, but the series brushes past his obnoxious antics underneath a cheeky persona. After a while, the actor's charisma softens my harsh perception of him. Nonetheless, I was wary of the relationship dynamics and couldn't understand why Q would entertain X initially.

Once the story gets into a comfortable groove, 21 Days Theory gains steady momentum over the next few episodes. The series shines as a sweet teenage romance with plenty of breezy banter and flirty encounters. Each scene highlights the easygoing rapport between the leads. I enjoy watching their relationship develop as Q and X become cozier. It feels rewarding when X flashes a warm smile or Q appears more relaxed around his love interest. 21 Days Theory conveys a budding schoolboy crush, and you'll believe these characters are growing fond of each other.

The casting is on point. 21 Days Theory chooses two charming actors who portray their roles authentically. X's actor (Bever) captures your attention with a bright smile, twinkling eyes, and genuine warmth in his expressions. This series is an excellent showcase for him, emphasizing his boyish and bubbly charisma. His costar (Tee) is also a decent performer who finds an optimal balance between playfulness and bashfulness in his demeanour. He matches his partner's vibe to produce smooth chemistry. They make a compatible couple who works well together.

21 Days Theory features several subplots with the supporting cast. Toy's secondary romance is a fine addition, enhancing the narrative with boisterous energy. Frank's storyline is less successful, and I feel uneasy about the dubious relationship with his tutor. In addition, the series depicts a sympathetic coming-out saga involving Q and his mom. While I appreciate the positive sentiments, these scenes may seem corny because the messages are too deliberate. The heavy-handed storytelling can use more finesse and subtlety.

21 Days Theory has a happy ending, although the last episode contains annoying conflicts. The tensions halt the brisk pace and disrupt the lively atmosphere. The finale commits the same mistakes as the start, where the writing seems contrived and clunkily executed. Sadly, the clumsy conclusion sours my feelings about the series, reminding me of its narrative flaws. Regardless, 21 Days Theory impresses me with its quirky comedy, endearing characters & cheery attitude. This delightful BL drama delivers a satisfying teen romance in a brisk and compact journey.


Lighthearted story

21 Days Theory is a lighthearted love story that overcomes a rocky start and develops into a relaxing journey. The breezy banter and flirty exchanges are amusing to watch.

Easygoing romance

Q and X make a compatible couple after moving past their initial awkwardness around each other. They have an easygoing rapport with many cute and charming encounters.

Smooth acting

The two young leads deliver smooth performances and share comfortable chemistry. X's actor (Bever) shines the most, exuding boyish and bubbly charisma.

Happy ending

21 Days Theory has a happy ending where the characters reunite after resolving their earlier disagreement. The last episode has some annoying conflicts that disrupt the lively atmosphere.

Cozy artistry

This series looks bright and vibrant with warm colours in a cozy aesthetic. The visuals look pleasant enough without being too overproduced.


21 Days Theory is an adorable BL series conveying a sweet schoolboy crush. Although the plot is somewhat flimsy, this delightful love story is packed with charm, cheeriness, and charisma.

21 Days Theory Episodes

Episode Guide

Q visits X at his condo after the injury.

21 Days Theory has a total of 4 episodes. Each episode is around 40 minutes long. It is a medium length BL drama, and you can finish the entire series in under 3 hours. 21 Days Theory started on August 7, 2022 and ended its last episode on August 28, 2022.

Episode 1
Episode 2

Episode 1

X and Q first meet in the acting audition in 21 Days Theory Episode 1.

Q is a high school student whose mother runs a bakery. The mom encourages Q to pursue an acting career. However, he hasn't achieved much success so far. Q meets X at the latest audition. This senior student goes to his school and competes for the same acting gig. X has a cheeky personality and teases Q constantly, making a terrible first impression. They have an embarrassing encounter in the restroom, where X mocks Q at the urinal. Despite their animosity, they share a cab ride home after the audition.

Q arrives at his home. X boldly introduces himself to Q's family, who invite him for dinner. X is a charismatic guest, turning on his cheerful charm. Q's mom and uncle like him a lot. Nonetheless, Q remains antagonistic. At the end of the episode, X proposes an unconventional competition. In the next 21 days, Q must find a way to approach Mook, a famous influencer at their school. He'll win this deal if Mook agrees to take him on a date at an upcoming awards ceremony. The competitive Q agrees to the contest, beginning a friendly rivalry with X.

Episode 1 review
X mocks the size of Q's manhood.

What's the point of this 21-day competition? The rules are so random and the prize is too vague. Why would Q agree to such a nonsensical rivalry with this guy he detests? Also, poor Mook gets dragged into the silly contest without her consent. Logically, a lot about this plot doesn't make sense to me. I understand the competition poses an excuse for Q and X to interact, but the scenario is a stretch.

My first impression of X is unfavourable. He disturbs Q in the restroom, gawks at his junk, and then mocks the size of his manhood. He also knocks Q on the ground and doesn't even apologize. X's behaviour isn't funny or cheeky. Instead, he comes across as a creepy asshole. Worst of all, Q has done nothing to provoke this animosity from a stranger. 21 Days Theory offers an unflattering introduction to its main character. I can understand why Q doesn't like him so much.

Why is X so mean to Q? Initially, I assumed he riled up Q to help him perform better in the acting audition. Then, I thought he wanted to provoke Q to make a memorable impression. The series never addresses X's behaviour in the first scene, brushing past the inappropriateness. X doesn't apologize, offer an explanation, or feel guilty about treating Q terribly. It seems like he antagonizes his crush without reason.

That scene with Toy kneeling in front of Q's crotch is a bit naughty, huh? 😳 I thought the moment was funny in an inappropriate way, provoking a small nervous giggle out of me. However, the imagery is surprisingly risqué for a BL drama I assumed would go the innocent and wholesome route. I notice a few other intentionally mischievous scenes throughout the series. The humour relies on the viewers' overactive imagination as they scandalize ordinary situations.

Episode 2

Q and X grow closer after an accident.

Q schemes with his friends Frank and Toy, devising a strategy to approach Mook. Frank helps him manage his social media messages with the celebrity influencer. Meanwhile, Toy suggests sneaking in treats in the classroom, making her curious about the secret admirer. Toy also follows Mook and even signs up for a fitness class to do covert surveillance. He stands out a lot, so she quickly notices his presence.

Q's newest scheme involves setting up a fake accident to introduce himself to Mook. His friends plan to bump into the pair, allowing Q to save the damsel in distress from danger. However, things don't go according to plan, and X injures himself when rescuing Q. Since X must wear a sling over his broken arm, Q feels guilty about what happened. His family invites X for dinner to thank him for his heroic act. Q's mom notices the chumminess between the two teens during the meal.

After the accident, Q keeps visiting X's condo to ensure he's doing okay. A casual conversation reveals that the high school senior used to study overseas and feels more comfortable speaking formally. Although Q still acts annoyed, his relationship with X has improved. The two teens begin to exchange cute text messages with each other. The episode ends with Toy introducing himself to Mook as he offers her treats. Even though Q is supposed to be the one befriending Mook, Toy has developed a crush on her instead.

Episode 2 review
Toy spies on Mook with a telescope.

This episode is casual and relaxing. Initially, I was skeptical about the competition angle, which seemed too random. However, 21 Days Theory takes a lighthearted approach, adding lots of silliness and humour to energize the plot. The goofy scenes with Q and his friends work for me. Every time Toy pulls out a telescope to spy on Mook, he looks so ridiculous that it's funny. The story is winning over me with its delightful charm!

Toy developing a crush on Mook is a cute twist. The typical narrative is Q courting Mook until she agrees to go on a date with him. However, Toy's romantic feelings introduce an unexpected curveball. At first, you assume a relationship would develop between Q and Mook. Then, the story takes a surprising detour with a Toy and Mook secondary romance. While I'm indifferent to a BxG couple in a BL series, I'm glad Mook isn't just being deceived in this arrangement. She has a real suitor genuinely interested in her instead of being a pawn in Q and X's competition.

Okay, I'm fond of X's character now. The actor (Bever) is super charming and convinces me of his sincerity. Whenever X smiles, his facial expression exudes a lot of genuine warmth. The writing also softens X and makes him more sympathetic. However, the bulk of the work comes from Bever, who does a stellar job at rehabilitating his character. I like this actor a lot, and his performance stands out among the cast.

Episode 3

Q and X have an argument in 21 Days Theory Episode 3.

Episode 3 begins with Q helping X wash his hair in the bathtub. They have a cute exchange before turning the tender moment into a water fight. Afterwards, Q takes care of X's arm injury. As they chat, X reveals he transferred schools frequently and doesn't have many friends in Thailand. Q returns home and feels happy about spending the day with X. Q's mom chats with her son, hinting he could confide in her about his feelings for X. However, he plays dumb and doesn't mention his crush.

Meanwhile, Mook and Toy continue bonding. She reciprocates Toy's advances and enjoys his company. Mook's sister Mild is Frank's tutor. Mild has been helping the younger student with his studies. Frank admires her intelligence and spunky personality, proving that he can learn outside of a classroom environment. She's also brave and fends off an aggressive man in the last episode. Mild already has a girlfriend. She seems uncomfortable after noticing Frank may have developed a puppy crush on her.

X and Mook are the school's representatives for SSEAYP, a student exchange program. They'll leave to study in Japan for a few weeks. Before the trip, X enlists Q's help to film a promotional video for the campaign. Q's uncle Man offers them a ride. Since Man acts affectionately around X, Q sees their interactions and gets upset. The two teenagers argue, but X insists he isn't flirting with the uncle. They make up with an embrace. The episode ends with Man questioning Q's feelings for X. Q is worried about coming out to his mom, but Man offers his support.

Episode 3 review
Q helps X wash up in the bathtub after his injury.

I really like the first scene in the bathtub. It's a cute bonding moment between the leads, highlighting their improved relationship. Based on Q's demeanour, you can tell he's getting cozier with X and warming up to his love interest. Before, there was an edge whenever Q talked to his former rival. Now, there's a flirtiness to their interactions that signifies a mutual attraction. Their rapport feels comfortable to watch.

I feel unsure where the series is headed with Frank and Mild's relationship, but that storyline makes me uneasy. The scenes are hinting a romantic angle, even though she already has a girlfriend. Each Frank x Mild interaction gives me anxiety, not knowing whether 21 Days Theory plans to straightwash her or not. Also, the shallow characters and their repetitive exchanges don't add much value. Frank and Mild aren't important figures. We can scrap their entire subplot and use the time for other developments instead.

Q is in the wrong for throwing a childish tantrum about X and his uncle. With that said, Man had moments where he seemed sweet on X, causing suspicion. I'm glad the uncle confirms he isn't attracted to a much younger guy. Let's not act like Kevin Spacey here. Also, I like the last scene where Q's uncle chastises his nephew for making inappropriate accusations. This conversation is needed to clear the air and reiterate the severity of what Q said. Their chat ends nicely with Man being a cool uncle, offering guidance, and mentoring a confused gay teen.

Episode 3
Episode 4

Episode 4

21 Days Theory has a happy ending where Q comes out to his mom.

Q's mom and uncle leave the house for a family visit elsewhere. They hope to patch up Man's relationship with his dad. Q and X are left alone to look after the house as they work on the video project. As Q eats a snack, his face gets messy. X uses his finger to point toward the smudge. However, Q gets the wrong idea and assumes X wants a kiss from him. Q shyly gives him a quick peck on the cheek. When Q's family returns home, they find the two teenagers playing video games. They haven't done anything inappropriate as the mom had feared.

This episode reveals X and Mook were in cahoots all along. X devised Q's competition to test out the 21 Days Theory. This psychology theory states that repeating an action can turn it into a habit after three weeks. Q overhears his conversation and thinks X's flirting is part of an experiment. He gets upset and refuses to listen to X's explanation. Later, Q's mom comforts her distressed son. He comes out to his mom, confirming his feelings for X. The mom offers unconditional support no matter whom he loves.

Happy ending
Q kisses X on the cheek in 21 Days Theory Episode 4.

21 Days Theory has a happy ending where Q forgives X over their misunderstanding. Earlier, Mook shows Q a video. The footage proves that X had a crush for a long time. He used the experiment as an excuse to become brave and act on his secret feelings. Unfortunately, Q couldn't reconcile with X, who had left for Japan already. The leads remain apart for two months. The final scene shows X returning to Thailand, as Q shows up at his apartment with bakery goods. X offers to pay for the treats with a kiss as the screen fades to black.

Meanwhile, Q's friends also clear up their conflicts. Toy and Mook argue over the 21 Days Theory, but they resolve the disagreement by the end of the episode. Mook brings Toy as her official date for the awards ceremony. As for Frank, he doesn't have any romantic feelings for Mild. She reminds him of his older sister, who died due to a disease. His deceased sister serves as his inspiration to become a doctor. Mild is touched by his story and agrees to continue being his mentor.

Ending explained
Q and X are in the bedroom together.

That kissing scene is an adorable BL moment, perfectly executed with an abundance of cuteness. The interaction is simple, but it still manages to be funny, sweet, and charming. This wholesome encounter proves you don't need overt sexuality to convey a romantic connection between two teenage leads. It might come across as BL fluff, but I think this might be the best scene in 21 Days Theory.

A less effective scene is when X comments on Q's morning wood. His behaviour is socially awkward, right? Typically, these crass boner jokes don't irk me in BL dramas. However, I'm more sensitive because X already had a history of improper remarks about Q's manhood since Episode 1. Until now, his character charmed me enough to overcome a lousy first impression. Yet, this moment reminds me of X's obnoxious personality again. 

I don't understand the contrived drama with the 21 Days Theory. Why is Q so mad at X? Maybe I'm speaking from a viewer's perspective, but X's intentions seem evident from the start. He's using this so-called competition to hit on Q. However, Q acts offended and won't listen to X's explanation. He creates unnecessary tension that drags down this finale. Also, I don't like the series ending with Q arriving at X's doorstep. I want to actually see the characters reuniting and reconciling in the end. This conclusion is too vague and doesn't make enough impact.

Q's coming-out moment in this finale is just okay. I believe 21 Days Theory has good intentions and wants to reinforce positive LGBT messages. However, the entire subplot with Q and his mom seems overeager. The series tries too hard to push this sentimentality, diminishing its effectiveness for me. The story arc lacks subtlety, a critique that applies to the rest of the series. Still, I appreciate that 21 Days Theory shows their support for gay teens navigating their sexuality. Despite a bit of clumsiness, their efforts are sincere and well-meaning.

21 Days Theory Information

Rookie Thailand

Rookie Thailand is a Thai BL studio that made The Best Story (2021).

Rookie Thailand is a Thai BL studio that made The Best Story (2021), 21 Days Theory (2022), Future (2023), and Night Dream (2023). It also produces several variety shows.

  1. I watched 21 Days Theory after I saw your recommendation and I really liked it. There is a sweetness to the story – Q's loving family, his supportive and accepting friends, the cute cheek-kissing scene – that I enjoyed. I loved how Q refers to himself in the third person sometimes (only referred to once in the subtitles, but it sounded like he did it quite often); X commented on how cute it was. I was more sympathetic to some of Q's outbursts than you are. Q is wrong to get mad at X when they are filming the video, but he would be justified in getting mad at Man, who has been inappropriately flirtatious with X from the beginning (even Q's mother – Man's own sister – had warned him about that earlier). That may just be how Man always acts, but it's a little creepy. And I thought the mean way X treated Q at first was part of the reason Q blew up later when he thought X was messing with him as part of an elaborate joke or experiment. It's a classic BL feature that the main couple has to have a break-up that could be resolved with a 2 minute conversation that they refuse to have, and I did not mind this version of it.

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