Man, trying to remember the whole cast of 'The Betrayal Knows My Name' is a trip because it gets so expansive. The core duo is Yuki Sakurai, the reincarnated empath who can see people's painful memories, and Luka Crosszeria, his overprotective Doberman of a guardian angel/reincarnated brother. Their messed-up, intense bond from a past life is the engine of the whole thing.
Then you've got the Zwei, this whole organization of reincarnated warriors fighting demons. There's Takashiro Giou, the stoic leader who feels like a dad to Yuki sometimes. His younger brother Kanata is the hot-headed one. Hotsuma and Tsukumo Renjou are the twins who provide most of the comic relief, which you need with all the angst. And you can't forget Jeanne, the badass swordswoman with her own tragic backstory.
The thing is, half the cast has two names—their current life and their past life identity from a thousand years ago. Luka was formerly known as Licht, for instance. The demons, led by the creepy Waldstein family, are major players too, especially Kuroto and Tōma. It's a huge web of past and present connections, honestly.