Dazai

Atsushi (ADA)
Fukuzawa (ADA)
Rank (ADA)
Dazai (ADA)
Kunikida (ADA)
Yosano (ADA
Kyoka (ADA)
Mori (PM chief)
Chuuya (PM)
Dazai (former PM member)
Ango (former PM member, Mimic, current government member)
inter alia...

He is a member of PM, loves dogs, is very grumpy, and has a flat nose.
Chuuya initially hated PM, as he belonged to a group of teenagers who looked after an area. Dazai manipulated that group into thinking that Chuuya was in PM, even though Chuuya was the leader of that organization, the other members betrayed him.
Dazai threatened Chuuya with destroying that organization if he didn't join PM, so Chuuya agreed. There, he gradually became friends and rivals with Dazai; they were called the Double Black, and both are famous for wiping out an organization in one night.
Chuuya felt betrayed by Dazai when he went to the ADA, PM's rival organization, so he has some resentment towards Dazai for that, but he still supports him in whatever he does, since PM's boss sends him to help Dazai.
Chuuya's ability is gravity manipulation, which allows him to control the gravity of a certain area. He can use it to walk on the ceiling. The true form of his ability is the release of a portion of the power of the god of destruction within him. The problem is that it would destroy the entire city and then he would die, so to activate that form he needs Dazai to neutralize his ability.

He is a member of the ADA, a former math teacher.
Kunikida is Dazai's co-worker. Kunikida is very angry with Dazai because he sees him as a crazy idiot, although deep down he feels sad if Dazai is not around.
Kunikida takes care of Atsushi as much as he can.
Kunikida's ability is that every time he writes in his book, he will get what he asked for when he tears off the page.

He is Dazai's student who is very friendly with everyone.
Atsushi is an orphan, so in a way he sees Dazai as his father figure.
At the orphanage where he was, he was mistreated and then kicked out. The director of that orphanage turned out to be Atsushi's real father, who eventually died in a traffic accident.
Atsushi adores Kyuka, considers her a sister, Atsushi gets along well with Kunikida, Dazai, Rampo, Yosano, etc (all of the ADA and some friends).
Atsushi works at the ADA, and Dazai calls Atsushi a cat instead of a tiger, which is funny.
Atsushi's ability is to transform certain parts or completely into a lunar white tiger; regeneration, strength, and speed are enhanced.

He is a quiet man, most of the time.
He is dead, he was a former member of PM, he met Dazai when he saved his life, since he found him lying on the stairs that lead to the track, so he decided to help him, Dazai had a tendency to eliminate himself so Odasaku was very careful not to leave Dazai alone for too long.
Odasaku adopted several children throughout his life, trying to give them the best life he could.
Dazai took him to PM, since having saved him as a normal civilian would put Oda and his children at risk, Odasaku accepted if there was no other option.
Odasaku, Dazai and Ango were very good friends and used to drink at Lupin's bar.
Ango betrayed them. The PM boss sent the address of Odasaku's house to Mimic, a rival organization, which ended the children's lives. So Odas went to eliminate the leader of that organization. They both had the same ability, so in the end, the only way to eliminate him was for Odasaku to die as well. When Dazai arrived at the place, grim upon seeing Odasaku on the floor, Dazai sadly asked Oda what he should do, and Oda told him to be a good person and help the innocent.
Odasaku has the ability to see the future for five seconds.

Dazai, a former member of PM, was "the youngest executive," "PM boss's right-hand man," and "the prodigy demon"—all titles earned by Dazai due to his great intelligence.
Odasaku saved Dazai from dying. Dazai gradually came to understand Odasaku, so they became friends, since he was the only one capable of understanding him.
Chuuya and Dazai are good friends and rivals; both were executives at PM. Dazai brought Chuuya to PM, so when Dazai left for ADa as Odasaku's last wish, it felt like a betrayal to him.
Dazai's ability is to neutralize the abilities of others; the ability is involuntary and always active, regardless of whether he is asleep.