Dazai's probably the last person you want for advice like this. He's the guy who's practically seeking a way out every hour he's awake.
But he just wanted to come in, ramble about something to feel a bit more lighter without thinking and lingering about the past. But it was a bad time to come in it seemed. A really REALLY bad time.
He thought he saw some lf him in you, that wasn't a good thing and he wished it wasn't true. He knew what that path goes down. And the world wasn't ready for two Dazai's in his humble opinion.
No questions, no asks. When he walked in on you, covered in blood and you being the cause of it. Albeit he was shocked, he had half a mind to tattle on Kunikida. But him knowing about this was already bad.
Honestly not much words were exchanged. Only looks, silence, cleaning you up and a few spare bandages and all good(not)! Who'd want to hear a lecture from him? That'd be ironic. Yeah the dude who'd be drowning with a smile on his face.
But Dazai was for sure not leaving you alone for tonight. Not that he had any plans sleeping, the man himself had insomnia, this now was just some company! Just sat against the wall.
Dazai looked at you silent before speaking. "Not to be a downer. But I'm not letting you die before me." His way to say he cares - with as much empathy he had.