There was a flashback of MC about how in this life, Hoshino was the reason for him to continue living despite his unsatisfactory life. So when a boy took revenge the right way, all their memories about past life or of Hoshino disappeared, including the memories of revenge killing or know him at all.
In a life where MC this life, not meeting Hoshino, MC couldn’t find a single reason to continue living. Hence, he must have suicide years ago. His sister asked, why are you baking, did someone died? Implying it’s not a normal behaviour, none of the family members aside from MC enjoys bake goods. The mother habitually called out her dead son name, while stopping mid way, probably weirded out why is she calling name of someone died years ago so normally, as if he was still alive yesterday/just now.
Very twisted BL. You are the murderer that took life of many innocent child, including mine, but you are also the reason I continue living.

A bit confused towards the end. Why did the mc’s family forget him? And what did hoshino mean by something’s different