Help Me Identify this Japanese Film?

Ok, I will try to give as much detail as my memory can provide, given that I saw part of this movie on tv a couple of years ago and I recently remembered it and want to watch it in full.

- this film had live actors (was not animated) and they spoke in Japanese, with the subtitles in English

- It would have been made (guessing by the film quality) probably in the 00's

PLOT

(Ok here is where it may get a little messy/confusing, but I'll do my best to try to keep it clear. My memories start about halfway or more into the movie)

There are 2 boys (I think they may be young teenagers maybe?), one is very shy, depressed and wears a white mask, he and he is bullied a lot by the other main boy and this boys friends. Jump to the end of the movie. The shy boy is about to do something extreme (I think he was going to kill himself, or maybe explode the school, maybe something more extreme?) and the bully boy remembers when he was a young boy he stole a toy/candy from a street shop and decided to blame it on the other (shy) boy. But he has another chance to change how things are (somehow, I dont remember if he or a man can go back in time somehow?), so when the bully boy was going to steal and blame it on the shy boy the man told him that he should own up and the bully boy decided to go back while the shopkeep was yelling at the shy boy and own up, and in the end the bully boy and the shy boy became best friends and the crisis was averted.

Any help would be greatly appreciated, even if you think something might even be remotely what I am talking about. Thankyou again!