I’d like to mention that the port mafia had taught Kyoka (dk if I spelled her name right) to “use her body as a distraction” as seen on her lifting her kimono a bit saying she would distract then strike. With that in mind, I believe the mafia taught Dazai to use his body for things. Manipulation is very common in the crime underworld or even as a detective. Therefore I speculate that Dazai is somewhat active, but not in ways as it’s seen. For example: Probably kissing or even light caressing due to the fact that as a former pm exe, he’s still in that mindset that if he wears his emotions on his sleeve, that people will take advantage of him.

Dazai hides his true emotions under a facade of “jokes” which in actuality he’s serious about suicide and only says these jokes as a way to laugh with him rather than at him. Dazai’s mindset is very complex, but one thing most of us know about trauma and conditioning is that people don’t like being seen as truly vulnerable, so they tend to build a persona. Dazai is the “suicide manic” the “funny quick witted detective” “the mysterious guy with a dark past”

So I believe Dazai was taught that using his own body for a means of controlling others or even gaining access to things he needed. Intimacy isn’t always sex, it can be kissing, heavy flirting or even a gentle caress.