Because the game is still in development, Senpai’s personality is not yet set in stone.

It is likely that some NPCs will have unique reactions to seeing a loved one get murdered. For example, if you murder a character’s sibling right in front of them, they may attack you regardless of their personality.

I imagine Senpai as the type of person who would normally be gentle and prefer solitude, but upon witnessing a masked killer, would feel enraged at the cowardly act of killing another person while hiding one’s own identity, and would unmask the killer without regard for his own safety – especially if the masked killer just murdered his childhood friend or little sister.