Curate, connect, and discover
We talk a lot about the cycle of abuse, but we need to discuss the savior chain more because, aside from being one of the most wholesome concepts in the entire series, it's also way more direct than the cycle of abuse and it's what breaks it.
Odasaku begins to save orphans because a man told him to write fanfiction and that led to him to stop killing. He told Dazai to become a good man because he knew for himself that yes, this is a more beautiful path, this makes life just a little bit more worth living.
Dazai saves Atsushi because he sees what Odasaku told him: a traumatized, helpless orphan. He saves him (at first) because of the promise he made to Odasaku, and the opportunity given to him on a silver platter to help out an orphan and give him a home (properly this time).
And on Atsushi's end, that means everything to him. The fact that for the first time in his life, he has someone who didn't give him up on him. That he now has a home, a place where he belongs.
And it's for that reason that he chooses to save Kyouka. He doesn't give up on her because Dazai never gave up on him. Because he feels empathy for her, and wants to bring her over to this new light he's discovered because someone was kind enough to show it him.
Dazai helps Atsushi because Odasaku helped show him the light.
And Odasaku told him to become good because a man once showed him the beauty of saving lives instead of taking them.
And it's this cycle that ends up breaking the cycle of abuse, this generation mistreatment of orphans because they see their own darkness inside of them. Instead, this cycle sees the light inside of others and it brings others to save another.