Somehow 18 (2017)

The synopsis reminded me of this Korean drama.

The main character, Gyung Hwi (28 male) is a university hospital resident. Back when he was in high school, he was bullied and attempted to suicide, however, Han Na Bi (a mysterious transferred girl) stopped him from dying. She ended up suddenly committing suicide after telling Gyung Hwi to live (not literally afterwards, but you get the gist).
For the past decade, he can't forget about her. However, one day, he wakes up to find himself as his 18-year-old self and it's a week before Na Bi commits suicide.
As the 18-year-old self, he was a loser, but he can't miss the opportunity to stop and save Na Bi from committing suicide. In order to do this, he has to find out what happened to Na Bi and the reason why she ended up killing herself, and of course, stop her from doing so.
Even though he is his 18-year-old self, he has the mindset and experience of a 28-year-old which will help change his gloomy past as he goes through his 18-year-old life.

"Will Gyung Hwi, who went back to the time he was an outcast, be able to save his first love and have a happy ending?"

I rewrote the synopsis from Dramalist's page about Somehow 18.

Closer to you is very similar to Somehow 18 just Closer to you is in chinese but somehow 18 is in korean.
Both female lead lean against the bus stop poles while listening to music,Both male lead is a outcast in school and both traveled back in time to save the female lead. Even the starting of Somehow 18 the scene is the same as Closer to you "ending".
Both female lead personalities is almost the same too and the way how they introduce themselves is so similar!!!

Although there are slight differences how the time manipulation works when comparing both dramas, they are about returning to a certain point in time. The protagonists fall in despair full of regret from experiencing something irreversible, and try to alter a tragic fate after being given another chance. A pure love story of an earnest attempt at trying to save the one they love.

Both are mini dramas in which one or both of the leads time travels back to their school days and tries to correct the mistakes of the past.

Both male leads try to go back in time to solve the regrets in their life. Again My Life's goal is to stop the bad guy before gaining a position in power and Somehow 18 goal is to save his childhood classmate.

These dramas both feature a couple going back in time to the prime of their youth after a tumultuous life in their late twenties.

In both movies, the main characters get the chance to travel back in time to change the lives of their important friends. Although the plot lines are very similar, Orange has a stronger friendship theme whereas Somehow 18 is mainly focused on romance

Both of them have similar plot i.e. time travelling, high school romance and going back to save their beloved one from a tragedy.

Both are dramas in which one of the leads time travels to the past/school days and tries to change the past to save the other lead who they loved and who died back then.

The protagonists try to save the life of a colleague who ends up dying, trying to change their deaths by traveling through time to try to find out why this happened.

There is time travel in Somehow 18, and the male lead knows about the future. In thirty but seventeen she was in a 13 year old coma, so she’s doesn’t know anything.

Both are mini dramas in which one of the leads travels back in time and tries to save the person they loved in school who died back then.

Both are short length dramas in which one of the leads travels through a portal/door to the past and tries to stop the other's death/disappearance back then. Both present time travel more like parallel worlds/timelines, and both have slightly ambiguous but happy endings.

The main lead gets a second chance to do things he regreted doing in the past.But this one he actually time travels back in time.

-Erased is also an anime that I highly recommend, since it would probably be less rushed than the movie. In Japanese, it is 'Boku Dake Ga Inai Machi'-

-both include male roles who are not the most popular in school
-both include time travel
-both are to save the death of a girl they like
-both have the sam vibes but erased is a bit more in the mystery category.