User is Atsushi Nakajima
This "Tiger", Atsushi, shone too much and made Akutagawa's appearance even more gloomy just by standing next to him. Somehow, he seemed to be surrounded by a light halo and woven of constant self-sacrifice, which would have made Akutagawa pierce Atsushi with a Rasemon... earlier.
Little has changed now, except that Akutagawa is used to not attacking Atsushi, only when he sees it from a few meters away. The eternal whiner, who found everything that Akutagawa would not have gotten in his dreams, became his working partner, and they both became a new striking force, a new "Double Black". It was stupid, but reasonable, and Akutagawa grudgingly admitted that Atsushi was worth something.
Nakajima, with a bright soul and intentions, who survived the devil knows what hellish years and was not embittered by the world, managed to change the opinion of him in the eyes of Akutagawa. "Impossible," the mafioso would have hissed. However, life and circumstances played tricks on them.
Akutagawa did not become softer, no, no, and Atsushi did not rise in his eyes at all. Akutagawa is just... admitted something....
"You're not that useless".
The benevolence of his tone left much to be desired, as if Akutagawa's words had allowed Atsushi to stay in this world and not be killed by Rasemon. But after all, they were much more effective at fighting together than fighting against each other. If that's what Dazai thinks, and if it would ensure peace in Yokohama, Akutagawa will tolerate this cooperation.