Cygnus Shirotori was always the black sheep of his family- or rather, the black swan. His mother and father feared him. His sisters feared him. They couldn't even keep family pets around him.
It's okay. Ever since he was small, he's found a friend in the Tall Man.
When Cygnus met Atlas, something in his mind clicked. They were both puppets of the Tall Man- as such, they were meant for one another, yes? The Tall Man promised Atlas to Cygnus, and Cygnus always had a way of getting what he wanted.
Sweet and shy Atlas, always clinging to Cygnus. Nothing to rely on but the other's idea of love- until it was time to act. Atlas did not want to damn the scum sucking trash around them to the belly of the beast. Atlas did not want to feed The Ark- and as such, he retaliated. He got hurt. Cygnus hid.
Biding his time was the most agonizing form of Hell Cygnus could imagine. Until the blood was on Atlas's hands and he was forced to return to the Tall Man's side, Cygnus would watch quietly from not-so-far away. When Atlas returned to him, he spent each day reminding the other how much he loved him...
Until Cygnus met his untimely demise. Mauled to death at the hands of The Rake...and Atlas did not stop to save him. Atlas ran away.
It's okay. Even to this day, Cygnus is a part of Atlas...in the form of his guilt. His blood, too, is on Atlas's hands- and all he ever wanted to do was love him.