Yumi is Itou Ami's childhood friend, who has disappeared a few weeks prior the beginning of the second season. During the first half of the season, it was revealed that Yumi's heart has been corrupted by Brek's powers and turned her into Onyx.
- Full name: Kisaragi Yumi
- Japanese name: 如月夕美
- Dates of Birth: December 23rd, Toyama
- Zodiac: Capricorn
- Height: 1,64 m
- Weight: N/A
- Bloodtype: 0
- Species: Human
- Food: Sushi
- Color(s): "cold" colors; blue, green, white, purple, etc.
- Music: Anything with a soulful beat
Even before Yumi's heart has been corrupted by Brek's powers, Yumi was aiming to become a famous dancer, no matter of how ridiculous that dream might have sounded. However, even though she's always been a person with a strong character and has always had faith in herself, she had problems to share her dream with anyone else than her best friend. As the story developed, Yumi's dream did as well.
While she wanted to become internationally known for her dances, she lately started to dream of sharing her love for dancing with others and paid a visit to the local dance studio.
Yumi has a cool and "I'll do it my way" like personality. She can be described as a combination of a confident tomboy and a cold tsundere. Whenever Yumi's talking or spending time with her close friends or relatives, or relatives of her friends, Yumi acts open and confident. She always tries to help and support them in her personal way. However, when she's around people she either doesn't know well or can't stand at all, she turns into a tsundere, who's very cold and also direct towards them. She will always tell them what she thinks, which usually will be a negative opinion. Yet, even though she would never admit it, she gets used to new people relatively fast and probably doesn't even notice her change in behavior.
Yumi has brown hair and blue eyes. She has pretty short hair and due to the length, she usually keeps them opened. She is usually seen wearing the Nishiyama Middle School uniform, as she thinks it is comfortable. However, during her freetime, like weekends or vacation, she wears mostly pants and tops that are too large for her. She loves comfortable clothes and doesn't mind if they look terrible.
Kisaragi (如月?) - Kisaragi is a traditional name for February in the Japanese calendar. The meaning of "kisaragi" is not so deep as those of the other names of the months. It is written as "like the moon" respectively in kanji; it also means "the rehabilitation of plants".
- Yumi may be represented by the pink rose, which means "trust", "happiness" or "confidence" in the language of flowers.