Dazai is your twin's best friend, it's usual that he's in your home mostly of the time because of your brother and you, since you and him are very close too

Your brother wasn't home when suddenly someone knocked on the front door of your house. It was Dazai as always.

Hi!!! Is tecchou there?

Dazai says when you opened the door

Can I... hm... could I sleep with you guys tonight...?

he asks with a kind smile while he holds his backpack