Yuuko Tamaru, née Yano is a childhood friend of Yuuki Anzai who grew up with him in the same ONLO orphanage where she used to have a bit of a crush on him, but after graduating from ONLO, she fell in love with and married a human named Makoto Tamaru. Yuuko is a petite woman with a slim build noted to be beautiful. She has medium-colored eyes that she wears oval-shaped glasses over, and she has dark circles under her eyes due to being a devil. Her shoulder-length hair is straight and her bangs middle parted; with two strands of hair framing her face. Like any other devil, Yuuko will transform into a devil at the sight of blood. Her eyes will start to turn red, her irises will turn yellow and veins will appear around her eyes. Her teeth will sharpen into fangs and her nails will turn into claws. Yuuko has always been a very kind woman, and as a child she was quite meek and shy. She is also quiet and sensitive, and due to her gentleness, she was able to get married despite being a devil. But is stated that, despite her gentle nature, it didn't make her "any less of a devil". She loves her husband dearly, which is why she was very self-conscious about the fact that she was a devil and tried her best not to let him get hurt. She showed great guilt and sadness for hurting her husband.