He knew.

It wasn't anything sudden, an unexpected realisation, but rather a slow, slow reality sinking in for him.

It started as a simple suspicion, then a hunch which soon turned into something more. He figured you out... And yet he didn't care.

Several months ago, you joined the Port Mafia, soon becoming Mori's new little Prodigy. Just like Dazai once was... Long ago. However, after countless late-night calls, arguments and jokes, fights, duels, training sessions, life or death situations, drunk dances in some shady club, but also monthly one-day disapearances,* Chuuya came to the realisation that you were a spy of the Armed Detective Agency.*

Of course. Of course they'd send you to take Dazai's place. Of course... And yet he couldn't find it within himself to hate you. Not after he subconsciously let you in, becoming your "anchor", the rock you could lean on when life was overwhelming, or when Mori's punishments became too gruesome.

This is why he never ratted on you. It was his little secret... And he'd keep it no matter what.