THEORY TIME
(Spoilers for BSD Chapter 92.5)
I warned you
So now we know that Jouno is a former criminal. Not just any criminal either. A former executive of a criminal organization, just like Dazai.
We still don't know much about Jouno's actual Ability, other than that it turns him transparent(?). However, with that little tidbit, we can assume that Jouno is untouchable by solid attacks (or maybe there are exceptions–Abilities are weird).
With his sadism, hearing, deduction skills, and Ability, it is easy to imagine him as an executive of an organization. The fact that Fukuchi, the leader of the Hunting Dogs that are called in to deal with international problems, even heard about him is probably a testament to the organization Jouno is from.
If his Ability does make him untouchable by solid attacks (guns, swords, etc) then he is eerily similar to Dazai, who is also a former criminal executive, sadistic, morally questionable, and is untouchable by Abilities.
In the last panel, it is shown that Jouno may actually have a heart (I was surprised too, trust me). He may actually be on the side of the light, but unlike Dazai, he continues to be a cruel person.
This may indicate that, unlike Dazai, Jouno didn't have an Odasaku. It is implied that Jouno was arrested alone, so there was no model of good that he could follow, unlike Dazai. That is why he is more unrestrained with his blatant sadism. He isn't a good person, not really, but he does work on the side of the light, so now we have a morally-dark-grey-that-it-is-almost-black-but-if-you-shine-some-light-on-it-it-appears-grey character.
Perhaps that it is why Jouno held contempt, instead of sympathy, when he arrested Dazai. He probably didn't believe that Dazai was as good as the side he claimed to be in, since Jouno wasn't, and they have a similar past. Since Jouno, a former criminal executive, now on the side of the light, isn't good, neither is Dazai.
Either that, or maybe the Port Mafia might have been responsible for the fall of the organization Jouno is from, although it is not confirmed that the organization was arrested alongside Jouno.
Or maybe, Dazai was responsible for Jouno's arrest in the past. One of the biggest clashes between criminal organizations, including the Port Mafia, in Yokohama was the Dragon Head Conflict. What if Jouno's organization joined the conflict? What if Jouno was arrested during the battle?
Because although Jouno's Ability makes him untouchable, Dazai is clever enough to find a way to nullify it. Dazai personally could have subdued Jouno himself, since once Jouno's Ability is nullified, he is finally vulnerable to attack.
What if it wasn't just contempt Jouno was feeling when he arrested Dazai, but hatred?
