Ruden was a normal domestic cat, who's soul was infused with that of a demon by a very high powered witch, it worked, but his soul was infused with that of a very low powered demon and was considered a failure. The demon allowed Ruden to be immune to magic from other demons. He had a much higher intelligence than a normal domestic cat and could communicate with any and all species. His owner was not pleased with how it had gone and went to abandon Ruden, Ruden was a very angry and aggressive cat even before being infused with a demon and while he had control over the demon when he became emotional it would make his emotions out of control, He attacked and killed his owner, brutally murdering her with his claws and teeth, ripping her to pieces and covering her apartment walls with her blood. When he regained control over himself he was saddened by what he had done, he wanted to hurt her for trying to abandon her but not to kill her, he took her necklace that she wore and put it around his own neck as a reminder of her, having that would remind him of the monster he could become so that when he looses control he has something to help him keep his emotions in check and a way of coming down after a negative emotional experience.
He then had to leave where he lived, the mystery of who killed his owner would forever be unsolved, he was then taken in by a young child living on the streets, who had ran away from home and had learning difficulties. She tied rope around Ruden's neck and kept him on a leash so he could not get away from her, it was so tight that his fur fell away and was always short of breath. She did not understand how to care for an animal let alone herself, she would poke Ruden's eyes and laugh, thus he has bad eyesight now due to repeated trauma there,
She put the bangles on his leg, pushed them on even as he yelped in pain as they were far too tight, so it is now impossible for him to take them of, she tried to pull his claws out but could not, so she filed them down so that they were tiny and blunt. The child then found used needless in the alley where she barely survived, and tried to jab them into Ruden, his anger finally took a hold and he broke free of her, he scratched her face but the necklace of his past owner allowed him to have control over himself not to take her life but to run away.
He soon found Deaus and helped her come to terms with what had happened to the both of them and they are romantically involved, he is more positive than her due to having a better control over his emotions and is more of a joker and she would be reluctant but eventually laugh at him, he was just what she needed.