[It's not just what Rena may know, but how she may take it, he can remember bits from other worlds but he isn't sure what Rika told her back home or anything. And he has yet to try to talk about it, he's worried to cause Rena to snap for his own stupidity.]

He's the older brother of another one of our friends, Satoko, though I don't think you have ever meet her?

[As far as he knows the only people to ever be present here were Rena, Rika and Hanyuu.]

Though I've just met him basically he's not a bad guy.