Forgetful | Kimetsu no Yaiba [boyxboy]

A story about about a man who is air-headed, he always tend to forget all the important things.
Until one day, all of it changed when he met the man who helped him change.
Everything was alright, he finally remembers things, he never forgets a thing.
Not until he witnessed something he can't forget, he suffered sleepless nights, trying to forget all about what he saw.
Two months have passed and he suddenly went out his room, happy.
He went to school but, he forgot all about the man he loved and loved him.

Why did he forget things all of a sudden?
Read this book to find out the events of his life, Tokito Muichiro's life being 'Forgetful'.