Adam no Rokkotsu
Oh my god...I loved this so much. It's about Rei who has DID(Dissociative Identity disorder) and has seven personalities that the main character interacts with. The story is more about finding who rei is, but each personality is so individual and I loved all of them. Some had different ages, one was a girl who loved fashion and sweet, but the main character loves all of them as well. (Romantically only for Rei though). Amazing, and the art is really good too. It was kinda sad, the personalities were created because of trauma :(
Replay (Tsukahara saki)
They have their own understanding of each other/ already know basically what the other feels, kinda like twins but not really. Love their personalities and the art, them moving in together later and the addition of baseball. 10/10
Sign