After seeing colorful and a mysterious voice tells him he's won a prize, a boy suddenly wakes up in
what appears to be a morgue. Not remembering anything, he tries to leave the room and scares
all the workers. Minutes later, he's sent back and a woman named Ruedee shows up by his side,
worried about his condition. The boy passes out and when he wakes up again, he finds himself in a
hospital room. He tries to escape, and as he runs down the hallway, doctors and nurses talk to him
using creepy stares and cryptic sentences. The elevator isn't working, so the boy climbs out of
the window, but the rain makes him slip and fall. A mysterious force stops him and makes him stand
on the side of the building as if it was normal. A window cleaner with the same creepy stare shows up
walking on the wall too and when the boy asks if this is real, the man hits him to make him
feel the real pain. This man is the Guardian, and he explains that the boy's a soul whose memories
have been erased before he was given the body of a teen named Min to live again. The Guardian
makes Min hold onto the edge of the window and makes reality take the right angle again,
so Min must climb inside. When he gets back in bed, a nurse shows up and is too forceful with
the needle, causing Min to accidentally knock off a water bottle. As the water freezes in the air,
the nurse reveals herself as the Guardian, who can take any shape they want. The Guardian calls
Min's body a "homestay" and explains that it's not permanent as they hand the boy an hourglass
that is counting the time the soul has to discover why Min ended things for himself. If in 100 days
he doesn't have the answer, he'll die again and never be reborn. Before leaving, the Guardian
reminds him not to let anyone know he isn't Min, and the water finally falls to the floor. The next
morning, a doctor comes for a check-up, and Min manages to pass it by saying his full name because
he read it from the sticker on the medicine, thus he's allowed to go home. Ruedee turns out to be
Min's mother, and at home Min discovers he also has an older brother named Menn that isn't happy
to see Min return. For now, Ruedee wants Min to sleep with Menn so he can be watched over,
he'll also wear Menn's clothes until they get him new ones. Menn overhears this and tells his mother
he'll be staying at a friend's tonight. Min asks his mom what happened the day he ended things,
but Ruedee doesn't want to talk about it. Next, Min finds his dad, who instead of welcoming him,
asks him to wait because he's on an important call for his MLM group, for which he quit his regular
job. When night falls, Min looks around the house while everyone sleeps. There aren't pictures of
him in albums or frames, and when he goes to check out his old room, he finds it locked. Min tries to
peek inside by looking under the door, but Menn finds him and sends him back. The next morning,
Min sees Menn leaving with two computers. Then he grabs a bunch of keys from the living room and
tries to unlock his room, to no avail. Min returns to Menn's room and climbs out the window to walk
along the edge of the building, this allows him to reach his own window and finally get inside. There
aren't any personal belongings around, only a few pieces of empty furniture and the framed picture
they used at his funeral. Seeing the death date shakes him to his core and causes him to drop
the picture to the floor, the noise gets Ruedee's attention and she finds Min red-handed. When he
asks what happened to his things, Ruedee explains he got rid of them. She wishes to know why Min did
what he did, it's then that Min notices the spot on the floor where the blood used to be. Crying
her heart out, Ruedee hugs Min tightly, asking him not to do that ever again. The following day,
Min goes back to school, and at least his mother got him his wallet back. In it he finds a curious
brooch and his mother's business card, she's an engineer that often has to leave town for
work. She didn't tell anyone in school about what happened, meaning Min's story will be that he had
the flu. Going back to class isn't hard because Min was a bit of a hermit and didn't have many
friends. The only person that approaches him is his best friend Li, who has a crush on him that
the original Min didn't return. Pi is in the card stunt club and so is Min, so he gets dragged to
the next meeting where the leaders remind him he needs to finish the drawing for the next
competition. Min immediately gets to work but gets distracted when he sees students wearing the same
brooch he found in his wallet. By following them he discovers the brooches mark the elite students
of the Olympics class, so Min puts his on and tries to join them, but the teacher knows he isn't
his student and kicks him out. Later, Min finds a note from his tutoring partner telling him to
meet her at the library. This is how he meets Pi, a beautiful girl that he quickly develops a crush
on just like the old Min did. After class, Min decides to use the card his mother left him to buy
nicer clothes and get a trendy haircut to impress Pi. Days pass with Min having a great time with
Pi. One afternoon, his dad comes by the school to remind him he has a meeting with the school
therapist and gives Min a bunch of his products to promote. The weird therapist begins asking very
awkward questions about Min's puberty before he stands up and swallows a lot of the products Min
brought. Suddenly this medicine freezes in the middle of the air and Min finally understands
this guy is actually the Guardian, who is here to remind Min to search for clues. He'll only
have one chance to answer, and if the answer is right the hourglass will stop. A few days later,
there's a festival at school and Min looks for Pi, only to find her crying over a practice test she
couldn't do. The pressure of the elite class is too much, so Min offers words of support to remind
her she's great. He also wonders if they're a couple, which Pi denies because he never asked her
out. Min invites her to the festival and they have lots of fun together playing games, making wishes,
and watching the fireworks. Pi mentions Min has changed a lot and doesn't look sad anymore,
then they hold hands. The next day, Min overhears his mother on the phone: apparently, his dad sold
her wedding ring to pay for more products for his MLM. To cheer her up, Min helps her cook
some durians, which he eats with no issues. This shocks Ruedee because Min used to hate durians,
but she's happy to see she's got a whole new son. She also shares some anecdotes of his childhood
that show how much she always took care of him even in the hard times. Some days later, Min must
complete a dare he had promised Pi for passing his exams. She puts a bunch of soap on his hair and
makes him run ten laps at the bridge, only to end up going with him for company. When they're done,
Pi gives him a gift because it's his birthday: it's a caleidoscope that she made herself. Pi
then confesses she likes this Min better, and the two of them kiss. Later at school, Min starts a
drawing of Pi at the bridge. While working in the club, he finds some pictures that show him
in the background next to a locker. Min rushes to force it open and sadly finds it empty, but
Li sees this and reminds him he left his laptop in her own locker with a note to give it to his mom.
When Li went to his house that day, Ruedee wasn't there so she left the laptop with Menn. At home,
Min searches Menn's bedroom. He doesn't find the laptop, but he finds the missing pictures with
his face scratched off on all of them. He also finds a bunch of paperwork indicating that Menn
wants to go study in Germany. Next, Min checks Menn's computer and finds a conversation of him
complaining about what Min did because now he has to stay with the family to support them instead of
going to Germany. Menn confesses that he hates Min and wishes he were dead, he also found his
goodbye letter in the laptop and hid it from his parents. Min then realizes that the second
computer Menn took with him when he left must've been his, so he goes to Menn's college to find it.
Menn catches him red-handed and says their family would be happier without him before throwing the
computer out of the window. Min immediately rushes outside and finds the laptop floating because the
Guardian is there, laughing at him before making the computer crash onto the ground. Min takes the
laptop home and manages to turn it on. The only file left is the goodbye letter, which explains
it was Min scratched his face off the pictures before mixing some shady medicine with soda to
make a deadly combo. The letter also says he hated his dad for taking advantage of his wife's salary
to stay in that MLM cult and that he hated how his brother was always condescending toward him,
making him feel small. He did love his mother, but it was frustrating that she was almost never home;
therefore the only light in his life was Pi. One evening, Min goes to visit Pi and he's shocked to
see her teacher getting frisky with her without Pi complaining much. The next day, Min interrupts
the elite class to punch the teacher and take Pi away with him. When Min confronts her on the roof,
he yells at her with fury, making Pi cry. She doesn't like the teacher, she only puts up with
him because it had been her only chance to join the Olympics team for a better future,
her career's what matters the most to her. Min thinks she doesn't need him, so he points at
the ground and tells her she should end things for herself. Later, Min's dad has to come over to talk
with the principal about what happened and wonders why Min can't be normal, prompting Min to call him
out for what he did to Ruedee's ring. Sometime later, Min decides to surprise his mother at work
following the address on the back of the business card, only to accidentally discover Ruedee has
been staying with a secret boyfriend. When Ruedee notices Min is there, she tries to explain things,
but Min runs away in tears. Back in his hometown, Min stays by the bridge under the rain, wondering
if he should end things again. The raindrops suddenly stop moving and the Guardian shows up,
wondering if Min has the answer. Min replies he hates this life and doesn't blame the real Min
for what he did, he blames the family and Pi because they can't be trusted. The hourglass
doesn't stop meaning the answer is wrong, so the Guardian reminds Min he has three days left. When
he returns home, Min smashes all the things in his room. Moments later, Li shows up to ask for
the finished drawing. Min's too annoyed to care and starts talking rudely to Li, telling her that
Min never considered her a friend and will never like her back, he also confesses Min missed school
because he tried to end things and didn't even mention Li in his goodbye letter. Li leaves the
place in tears. In the evening, Min and his dad go pick up Ruedee when she returns from work. She's
tired and wants to go home, but Min insists they should go out to have dinner together. He also
mentions he visited her at work to make her feel guilty. At the restaurant, Min leaves his parents
alone by pretending to go to the bathroom, but he spies on them and notices his dad returning
the ring. Instead of being happy, Ruedee finally confesses her affair. The dad leaves without them
and now Min and his mom are alone in the car. Crying, Ruedee apologizes to Min and explains
she broke up with her other boyfriend so she can always stay with her family. Min refuses to accept
the apology and tells her he isn't her son, her real son died because she was a bad mother. An
argument starts between them and this distracts Ruedee from seeing the other vehicle coming, thus
a car crash happens. Hours later, Min wakes up in the hospital. He immediately goes to check on his
mother, who is still unconscious, and Menn shows up to explain she's in critical condition. The
dad told him what happened, and Menn wonders why Min didn't tell him instead of ending things since
he would've helped him deal with it; he thinks Min needs to stop thinking nobody loved him. Min's not
hurt and is sent home, where he finds the durian dessert Ruedee left for him and the caleidoscope
Pi gifted him. Min realizes he's been acting very selfishly and makes it up to his club by finally
finishing the drawing. The next day, the Olympics team announces they'll be joining a very important
tournament. Pi is supposed to give a speech, but seeing Min in the crowd makes her feel guilty
and she runs away. Min finds her in a classroom about to do something stupid with a glass cup,
so he apologizes to her and hugs her, explaining he had been angry the other day and talked without
thinking. Pi shouldn't be disgusted with herself because it all was the teacher's fault. Feeling a
bit better, Pi finally goes to the principal to tell her about the teacher's abuse. Since it's
too late to practice a new design, Min leaves the drawing for Pi with a message of support.
Afterward, Min goes to see the card stunt club rehearsing. He apologizes to Li, explaining
she had been the only one to be nice to him and he never appreciate it. Li accepts the apology
and confesses that since Min didn't bring a new drawing, she gave the team one of his old ones. To
Min's shock, the team suddenly forms a drawing of Pi at the bridge that looks exactly like the new
one. Memories start flooding Min's mind as he runs away. The previous Min's life flashes in front of
him, showing him all the good times he had with his dear family and Pi. Min falls down the stairs
and the hourglass, now frozen, falls from his pocket as Min suddenly reappears in his room with
the Guardian taking the shape of his reflection. Min has finally understood that he isn't a random
soul, he's the original Min, and he died because he didn't know how to appreciate the good things
in his life, it's all his own fault. The Guardian congratulates him for winning and explains the
test had only been a way to make him see the truth - Min won't be reborn anywhere else, he can keep
this life. After the Guardian disappears, Min wakes up in the school again and the hourglass
is gone. Li checks on him and Min hugs her to celebrate before rushing to the hospital to find
Ruedee has woken up. She explains she and the dad are getting divorced, so Min can help whom to live
with and she won't blame him for choosing the dad because she hasn't been a good mother. Crying, Min
apologizes for his actions and swears he'll never regret being her son. From then on, Min returns
to his daily life. When Pi sends him a message showing she's won a medal, he fulfills his part of
the deal and runs a few laps down the bridge with soap on his head and only wearing his underwear.