Enough times for Chuuya to pick up on that pattern. The pattern, may I remind you, that doesn't have evident correlation to either nervousness or worry to most people. One that can even be interpreted as misplaced given the situation.

Which means that Dazai has done this in front of Chuuya so often, that Chuuya at first was hella confused, before he finally made a connection between when and why it happens. And still remembered that connection after four years of separation. Which gets us to my point:

What if this isn't the only emotion Dazai displays weirdly?

What if he has multiple unconventional patterns he displays for sadness, frustration, content, or disgust? The times he really feels them, and they become too strong for him to just deal with normally? What if these are the only times he's actually being genuine with his emotions?

And Chuuya is the only one who is familiar with them all?

Dazai would be jumping rope and Chuuya would be like, "quit sulking, let's get icecream"

Dazai hanging upside down on the couch and Chuuya going, "It's okay, mackerel. You can cry."

Dazai actually crying, full on heart-wrenching sobs, and Chuuya unironically going, "What, good news?"

It's just... comforting, for one person in Dazai's life to read him like a book. Everyone else would look at him like he's crazy, displaying wrong emotions/behaviors at the wrong time, but Chuuya knows that it's just how he processes feeling properly, and thus he's the only one Dazai can count on to put things into context and understand, which makes him display them even more openly.

🖤🧡

enjoy :DDD