|Japanese name:||五河 士道|
SpoilerShidou has the ability to seal a spirit's power. 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 space quake from happening he'll seal the spirits powers with a kiss in order for them to co-exist with human.
Shidou met her real sister at volume 3 which was Mana Takamiya. Shidou, Mana and Kotori can't remember much about what happened 5 years ago because a certain "spirit/person" locked their memories away, and at that time Shidou met Origami and helped her which was the cause as of why Origami fell for Shidou.
Once the power of the spirit is sealed within Shidou, he has the ability to use some portion of it, thus his resurrection power is from Kotori's abilities when he sealed Kotori's spirit 5 years ago.