coco's Questions (2)

there’s one that i can’t remember the name of where there’s a scene that the two main characters are in school and one of them is like a popular guy and he puts something like magnesium in the toilet and blows it up with his friend and the mc who’s like quiet is watching them get told off for it.
sorry if that doesn’t make any sense but if anyone has any idea what the manga/manhwa is called please lemme know cause it’s been annoying me.

It's about a guy who played the guitar, (I think it's guitar) and he meets a ghost in his apartment who convinces him to play it again.
Then he meets someone in the apartment next to him who exorcises the ghost and afterwards the mc goes to the ghosts hometown and talks to the ghosts unrequited love. It was also really sad if that helps.
Sorry if that was a bad description :)