When Nanno encounters a boy who likes to fool around with different girls, she decides to teach him a lesson he'll never forget. In Nanno's new school, a pregnant girl named Petch walks by, eyed by her schoolmates. Then, the guy who got her pregnant, Nanai, walks past her as if she's a stranger.
But when it's Nanno who walks past Nanai and his best friend, Jheng, he turns to look, finding the next girl to take advantage of. In their classroom, Nanno introduces herself, all while Nanai and Jheng stare intently at her. When the teacher thinks of a seat for Nanno, Nanai jokingly kicks Jheng, his seatmate, to make room for the girl.
Although the teacher ignores Nanai's suggestion, he still considers it a win as he's made Nanno laugh, which is more important. Beside Nanno is a girl named Lookmhee. Spotting Nanai staring at Nanno, she warns the new girl to not fall for him as he's already gotten many girls in the school pregnant.
The school turns a blind eye thanks to Nanai's popularity and the fact that most girls choose to terminate their pregnancies. Finding this interesting, Nanno jokes that she'll be okay as long as she doesn't get pregnant, but Lookmhee just looks concerned. At lunchtime, Lookmhee complains to a girl named Pin that although she invited Nanno for lunch, Nanno wanted to eat with Nanai.
Jheng comes to the table, but Nanai signals him to leave, so he's forced to eat with Lookmhee and Pin. But to Pin, Nanai's so charming that if he'd spoon-feed her as he does with Nanno, she wouldn't eat with Lookmhee either. However, Lookmhee knows Nanai will dump Nanno as soon as he gets inside her pants.
Upon hearing this, Jheng decides to make a bet, asking the girls how many days they think it would take for that to happen and annoying Lookmhee. But when Pin joins the bet and Nanno and Nanai walk past them, being excessively sweet, she changes her mind and thinks the two won't last long. Then, Pin and Jheng laugh.
In class, the students stare at Nanno and Nanai. When they leave, Jheng comes and entices everyone to join the bet. And so, the bet begins.
During the first day, in judo class, Nanai overpowers Jheng amid cheering from the ladies. But their enthusiasm dies when Nanai walks past them to Nanno, taking a sip from her water bottle. On the second day, Nanai's in a photo shoot with a trophy for the school magazine when Nanno interrupts to kiss his cheek, annoying the photographer.
On day 3, while Nanno and Nanai are wrapped in their own world over lunch, Jheng collects the bets of the students at the surrounding table. But when he spots Petch eating by herself, he skips her. Later, Petch finds Nanno after throwing up in the ladies' room.
She approaches Nanno carefully to strike up a conversation, informing her that everyone's betting on how long it'd take for Nanai to get into her pants. But instead, Nanno asks Petch how long it took for Nanai to get into hers, causing her to apologize for being so nosy. In her defense, Petch doesn't want Nanno to end up like her.
As she's about to go, Nanno retorts that self-pitying won't do her any good. Unsure about what to say, Petch just chuckles before quietly leaving. Afterward, Nanno makes out with Nanai in the locker room.
Then, Nanno asks Nanai to recall the exact days they've known each other, which is just a little over three days. Nanno tells him they still don't know each other well enough. To change Nanno's mind, Nanai sweet-talks her, saying love has nothing to do with time.
After all, he knew he liked her since the first day. He also adds he'll do anything for her. Just to tease Nanai, Nanno thinks it's still too soon, asking him to wait for another minute.
With the minute almost over, Nanno counts down from ten. Nanai then finishes the countdown for Nanno, and they kiss passionately. Nanno takes control and pins Nanai against the lockers, eventually kneeling and unbuckling the guy's belt.
Later, Nanai proudly shows Jheng the kiss mark he got as a badge from the encounter. The two friends chuckle as Nanai sets a new record for getting into a girl's pants—3 days, 3 hours, and 33 minutes. Now that the two have done the deed, Jheng unloads the pile of money in front of everyone to see who won the bet.
Lookmhee tells Jheng to get on with announcing the winner, so he begins reading the guesses that are too unrealistic. But suddenly, Nanno arrives and asks what's going on. Everyone hushes as Lookmhee stands, stammering apologetically for joining the bet.
Then, Nanno asks Jheng about his bet and claims it's nothing to be ashamed of. As everyone shuffles uncomfortably, Nanno decides to join in the announcement of the victor. She reads Lookmhee's guess, saying she's wrong but pretty close.
After that, Jheng hesitantly reads the next entry, which got the exact time. Impressed, Nanno asks who the bettor is, and to everyone's surprise, it's Nanno. While Nanno's taking the money, Nanai enters the room.
Nanno warns her classmates that, just like Nanai, she is also a player. She leaves everyone muttering behind as she marches straight up to Nanai, with money in hand, telling him he got played. Humiliated, Nanai looks at her furiously.
Later, during judo class, Nanai's head is elsewhere, giving Jheng the easy win each round. Jheng makes fun of his being rusty after spending time with Nanno, asking inappropriate questions about the girl. Nanai brushes him off, but he suddenly feels some pain.
Despite Jheng suggesting to call it a day, Nanai insists on one more round. Afterward, in the restroom, Nanai's regaining his composure by the sink when Nanno arrives and charms him, asking if he's mad at her. Frustrated, Nanai grabs and begins kissing her, all while Nanno looks sorely unimpressed.
He removes their undergarments and prepares to take Nanno from behind, but Nanno just taunts him because he can't get himself in the mood. After another failed attempt, Nanno mocks Nanai, saying they can just do it next time. Embarrassed, Nanai puts his undergarment and pants back on before angrily leaving Nanno behind.
Outside, their classmates are eavesdropping. Suddenly, Nanno comes out of the restroom and stops Nanai from walking away, acting like a desperate girl. Nanai says he wants to break up, causing everyone to whisper.
Although Nanno pleads that she can change, Nanai just dismisses her because he doesn't like the way she looks at him. Nanno still doesn't understand Nanai, so the guy explains she objectifies him. Then, Nanai reminds her they were just having fun.
When Nanai turns to leave, Nanno laughs hysterically, revealing she's just making a scene to make him feel like a man. At the same time, Nanno points out that he objectified her too. However, she doesn't feel anything, but she says maybe after that day, Nanai will start feeling something inside him.
During lunch, Petch sits beside Nanno, who's eating by herself. She thinks Nanno's strange because she's not like other girls. Petch confides she realized too late that Nanai wouldn't take responsibility.
When Nanno asks her what she feels about keeping the baby, Petch admits being happy. Nanno asks if Petch wants Nanai to take responsibility, but she just dismisses the question. At this, Nanno smirks devilishly.
Later, in the shower, Nanai notices that something has changed in his body. Afterward, he decides to make out with Lookmhee in the locker room, but as he unbuttons his uniform, the girl looks down and suddenly screams. With Lookmhee leaving him alone, Nanai looks down, too, and sees his belly has gotten bigger, surprising him as well.
Back home, Nanai joins his parents for dinner with a jacket on while holding his belly. When his father asks why he's wearing a jacket, he says he's just a little cold and assures his parents he's fine. He then starts eating, but he spits out the food on the table and thinks his favorite food is disgusting.
He blames his mother's cooking for feeling sick, and it isn't long before he gets up to throw up. The next morning, Lookmhee shares with her classmates, including Jheng, the incident she had with Nanai. But they all hush down when Nanai arrives early, his bag covering his belly.
Jheng sits beside Nanai and asks him if he will practice later, but he just shakes his head. As soon as Jheng eats his food, Nanai rushes to the window and throws up. Shocked, Jheng asks Nanai what's wrong.
But when Jheng comments about Nanai's belly getting bigger, Nanai snaps and demands to be left alone before storming off. In front of a mirror, Nanai stares at his growing belly. This makes him uncomfortable, which shows during his photo shoot with the school photographer.
Because of the photographer's flirtations after the shoot, they fool around in the darkroom. However, the photographer accidentally leans on the light switch and turns the light on, seeing Nanai's big belly. She, too, freaks out and leaves him alone, frustrated.
Gripped by self-consciousness, Nanai goes to the doctor. Thanks to the ultrasound, the doctor asks Nanai if he's had surgery before because it appears he's pregnant. The possibility startles Nanai, who reminds the doctor that he's a man.
But to the doctor, Nanai might be someone who's born with both male and female reproductive organs. In fact, his baby's a healthy girl he's been carrying for about 16 weeks already. Nanai stares at the doctor and the monitor in disbelief when he suddenly feels his baby kick inside, startling him.
As the days go by, Nanai finds himself getting more ostracized. He hears the photographer gossiping about the incident in the darkroom, and he gets so pissed that he slams his bag on the table and leaves. Jheng goes after him, justifying his presence in the gossip groups because he just wants to know what's happening in Nanai's life.
He asks Nanai to just tell him what's happening so he doesn't have to hear it from others. When Jheng suggests going to a health clinic, Nanai snaps and reveals he's pregnant. But just then, Nanno calls Nanai's attention and asks him to smile for the camera.
Realizing what Nanno's doing, Nanai hurriedly leaves. Unfortunately, it's too late. Around school, the video Nanno recorded has spread like wildfire.
Students are making fun of Nanai, with some believing he had it coming. All around him, Nanai's life is crumbling. He's even forbidden from running as student president.
Students are also disgusted when he throws up in public. Later, Nanai stares at his huge belly in front of the mirror. Then, he's haunted by visions of the girls he was involved with.
One says he's probably just sick, and another asks him to take some pills, just like what he told her to do. There's also a girl who offers to take him to a place where he could terminate his pregnancy, the same place where he took her before. In the end, Nanno comes and mockingly congratulates him for having a daughter before leaving him all alone in the dark.
The visions overwhelm Nanai so much that he throws his laptop away. Returning to school the next day, Nanai wears a thick jacket to hide his belly. But as he gets some of his things from his desk, students watch him struggle.
Nanai then leaves, with Jheng calling after him. However, only Nanno's call catches his attention. She mocks him and jokingly assures him she's not put off by his pregnancy.
Unable to handle the negative attention, Nanai leaves. In his room, Nanai stares at himself on the magazine cover and reads through the pages that describe him as a model student, crying. Then, his father knocks and asks if he's really pregnant.
He also expresses his disbelief that Nanai got himself into that situation. Enraged, Nanai opens the door and tells his father not to say anything if he's not going to help him. Sadly, his father replies that he's nothing but trouble.
Before leaving, his father tells him to terminate his pregnancy or never bother coming home, exacerbating Nanai's feelings. Nanai retorts he never said anything when his father got his own secretary pregnant and had her terminate her pregnancy too. When all's said and done, Nanai's left alone, crying in his room.
He decides to move out and rents a room somewhere. In the dark, he eats his food but just spits it out. Frustrated, he punches his belly and regrets it because of the pain, causing him to groan in bed.
In front of a mirror, he loathes his reflection. Afterward, he decides to take a pill, which he just throws up. In another attempt, he takes more pills, but he later throws up blood and gets incapacitated by extreme pain.
When Nanai awakens in the bathroom the next day, the despair drives him to clutch a knife. He puts the knife over his belly, ready to stab himself, when a knock interrupts him. Drpping the knife, he spots a figure outside the window.
Nanai stands and struggles as he heads to the door, but he only sees a girl with a red ribbon by the gate, already leaving. On the floor, however, is a card with two questions about his pregnancy. Upon reading them, it makes him wonder how he got pregnant and thinks of the last person he slept with: Nanno.
And so, disguising himself as a woman, Nanai waits for Nanno outside the school. He pulls her aside and demands to know what she did to him. But Nanno just uses his words against him, saying they were just having fun.
Then, Nanno leaves him behind. Later, Nanai follows Petch while he's still in disguise. He calls her and starts walking slowly, struggling and apologizing for everything he did.
Now that he understands how Petch feels, he's utterly regretful that he made her go through that situation alone. But Petch just stands there, assuring Nanai that since that happened ages ago, she's not mad at him anymore. Instead, she thinks they were both to blame for what happened back then, but Nanai disagrees.
Besides, Petch is happy with her decision. She reaches out to hold Nanai's hand, and Nanai hugs her. Finally, Petch bids him good luck and leaves him with a smile.
Sometime later, Petch goes into labor. Thankfully, after the pain and struggle, she successfully gives birth to her child. Meanwhile, Nanai also goes to the doctor, but he intends to terminate his pregnancy.
After the doctor injects the anesthesia, Nanai suddenly finds Nanno beside him, with a scalpel in hand, telling him he'll wake up in no time. He struggles as Nanno poses the blade over his neck, but his resistance just ends when everything fades to black. However, the nightmare comes when Nanai awakens.
The doctor gives Nanai his baby, which freaks him out, saying he wants to get rid of the child. He also points out that he was only a few months pregnant, but the doctor states he carried his baby for the full term. When Nanai reiterates he wants the baby gone, the doctor replies he can do it himself.
And so, back in his room, Nanai struggles with the baby crying beside him. Frustrated, he decides to strangle his daughter. But with his hands just a few inches from the baby's neck, he hesitates and begins crying when his daughter coos at him.
Nanai can't bring himself to kill his child. Instead, he chuckles through the tears when he notices wet spots on his shirt, realizing he's producing milk. So, he carries his daughter and breastfeeds her, all while crying and apologizing.
Just then, someone knocks on the door. Carrying his baby, Nanai opens the door and finds Nanno outside, who kisses his daughter after thinking she's cute. Nanai's glad to see her, and he apologizes for what he did and vows to become a better man.
All he wants is for her to come back. But Nanno just stares blankly, turning Nanai down as she only wants to gift him with baby supplies and check if he's a good parent. Seeing him step into the role has put her mind at ease.
Despite Nanai's pleas, Nanno closes the door and walks away. That's when she finds a photograph of herself with scribbles all over it. Realizing more similar photos are on the floor, she throws away the picture and continues walking.
Nanno sees that some of her photos are even taped to the walls, and as she follows them, she eventually reaches the rooftop. The last picture she sees is of her and Nanai, just minutes ago, with her face all scratched out. Then, a red ribbon flies to her shoes.
On the wall in front of her, she finds a message painted in red that says, "See you soon.
