The main protagonist of the story, Shidou is a student of Raizen High School. He was adopted into the Itsuka family when he was "abandoned" by his mother. He possesses a strange power that allows him to seal the powers of a Spirit in his body with a kiss; however, the seal will only work if the Spirit holds enough trust or affection toward him to allow it. Although considering trust and affection is a two-way street he probably needs to have a certain amount of affection too, or at least genuinely want to help the spirit from the bottom of his heart which he usually does even before seeking out a spirit.Due to this power which was already known by Kotori Itsuka he was recruited—or rather forced—to join "Ratatoskr" to help and save Spirits. Instead of killing Spirits to prevent spacequake from happening, he has to seal the Spirit's powers with a kiss in order for them to co-exist with humans.Shido has the mysterious, and unique ability to seal the powers of the Spirits into his own body, which was first discovered sometime in the past when Kotori was turned into a Spirit. To use his ability to seal a Spirit’s power, the Spirit in question must meet a certain condition or requirement. Those conditions or requirements are that, the Spirit in question must show affection, trust, closeness, and/or intimacy towards Shidou. Once these conditions of affection are high enough between Shidou and the Spirit in question, he can seal their power by kissing them on the lips.Depending on the Spirit itself and how much power they originally had, Shidou can either seal a majority of their power or all of it. Shidou can also “borrow” the power of a Spirit he sealed, but it depends on how close or intimate he is with that Spirit. This explains the nature of his regenerative abilities. However, it seems that using a Spirit's power (other than regeneration) taxes his body with great pain.A (seemingly) normal sibling relationship, Shidou deeply cares about Kotori (as a big brother) to the point that, he believed a fake promise made by Kotori which is no matter what happens, even if there's a spacequake, she will wait for him at the family restaurant. Shido shares an especially close bond with Tohka that goes beyond the level of mere friendship. He was the one who gave Tohka her name, based on the day of their first meeting, April 10th. Shido cares very deeply for Tohka, as shown on many occasions, always going out of his way to make her happy and teach her the ways of the world. In fact, his feelings of caring towards Tohka is so strong that, when she was captured by DEM, Shido prioritized saving her above all else, despite the grave risks involved and the enormity of the odds stacked against him.To date she is the only spirit he has failed to seal, however, she has indeed fallen for him, arguably before he even started to date her, and is something of a Yandere towards him. She is also very teasing, especially after she witnesses Shidou having to dress up as a girl to deal with the Spirit, Miku, and openly jokes about it, much to his dismay.Friends, acquaintances, and/or classmates, depending on which one he talks to. But overall, he usually has a mundane or normal relationship with any of his classmates. After Tohka and Origami began competing over Shido, however, many of his male classmates became very jealous of him.