Hakuya Mitsumine (三峰 白夜 Mitsumine Hakuya?) is the fiance of Kobeni Yonomori who suddenly appears on her 16th birthday with Mashiro Mitsumine (Hakuya's youger sister). He and his sister start living in the same house as Kobeni and Benio Yonomori (Kobeni's sister).
Hakuya is a tall man with spiky black hair that has bangs covering his right eye due to the scar which he obtained when saving Kobeni Yonomori as a child. He can only make out light but he is used to it. He doesn't tend to show a lot of emotion and his classmates find him scary.
Later, Hakuya is revealed to be an Inugami who possesses some rather unusual abilities such as an inhuman speed and endurance, allowing him to jump long distances. He also states that he can shapeshift into a black dog but refuses to do so. He sleeps a lot as he needs to make up energy in place of his missing power, used to save Kobeni.
Hakuya appears to be a calm, quiet and serious guy whose personality remains on a small known intelligence. He is a taciturn and mellow character where it is a bit oblivious to the world and slow to catch up on things. It is mentioned by Mashiro Mitsumine that he usually does not like sweets, but still ate it because Kobeni Yonomori made it. Although he doesn't show his emotions through expressions, Kobeni can usually tell what he is feeling.
He is shown to have patience and control over himself most of the time, rarely showing any kind of reaction or emotions to his surroundings.
He is overly protective of Kobeni. For example, he constantly follows her and on one such occasion, he goes to the super sale for her. He becomes happy with any little thing Kobeni does.
Kobeni is Hakuya's fiancée and childhood friend. They used to play together as children when Kobeni visited his homeland in the mountains, though Kobeni did not initially realize it was him since he was still in his Youma form as a black dog. During that time, Hakuya lost sight of Kobeni for a brief moment before she fell off a cliff, almost losing her life. Regardless of having his right eye scarred from falling off the cliff with her, Hakuya passed on half of his inhuman power to her in order to save her life. As a result of passing on half of his powers Kobeni was left with a weak constitution because his powers were not completely compatible with her body, resulting in her experiencing episodes of illness and fevers, seen multiple times in both the manga and anime. Nonetheless Kobeni lived through the experience thanks to him.
It is stated by Mashiro many times that Hakuya was raised to become Kobeni's future husband and has no objections against the idea. Because of his dog-like nature, Hakuya is protective of her and follows her around, always keeping an eye on her and helping her whenever he can. He had also flat out said that he liked Kobeni when her friend, Mayura, asked him what he liked in attempt to help Kobeni figure out what to give him as a Valentine day present during episode 4. Also, though his outward appearance does not show it, he actually gets extremely happy whenever she reciprocates his feelings through her little comments and actions.
Mashiro is Hakuya's little sister. Because of his blunt personality, Mashiro is very vigilant towards him and explains many things that Hakuya can't understand. This causes Mashiro to move in to the Yonomori's household alongside him. Mashiro has shown to care for her brother and often seeks him out for protection from Benio.
Mashiro is also Hakuya's love adviser and helps him to understand many facts about Kobeni that Hakuya himself can't understand such as finding a present for her.
Benio is Hakuya's future sister-in-law. Benio has shown to be jealous of Hakuya and can't get along with him because of the idea of him taking her little sister away from her and her own siscon personality. Despite her aggressive nature towards Hakuya, he doesn't seem to care and ignores her.
Shirayuki is Hakuya's mother.