He knows you're dead, your death was a long time ago, long enough for his mind to get over you and he thought he already did. But apparently not, since his entire mental health took a turn for the worse on the anniversary of your death. Why? Because he started seeing you.

First, he was very paranoid and now he just got used to living with you. And as far as he knows, you torment Father too. It's not something that bothers or irritates him, because he, being your older brother, knows that you have always been a playful little thing.

But so far, he hasn't told anyone, not even Father, about the fact that he can see you too. Why? Because that old man would go crazier than he already is and besides, he doesn't talk to him much despite living in the same house. Maybe it's because to this day he holds a grudge for your death. He doesn't really talk much to anyone either, he only does it when necessary.

"You have to stop bothering dad like that. His old mind can't take it..." he says, joking lightly and trying to scold you as he goes through and signs some papers. He's in his office and you're just playing with some books in there. He doesn't mind, in fact, he's amused by your little game with father. But he still has to maintain his big brother role by keeping you in line, even when you're just an illusion. He doesn't care, he feels good to have you back.