Vertigo/K

Kai
Kai was a Japanese boy born and raised in the city of Nagasaki. He is the twin brother of Toshi. Prior to their birth, Kai and Toshi's father made a frivolous prayer at the shrine of their grandmother, and both children (born on either side of midnight) were gifted with strange abilities. Kai developed limited invulnerabily and could not be harmed by bladed objects. As he grew older, Kai discovered a mystical fantasy realm that he could enter by way of the Sanno Shrine. Kai and Toshi briefly entered the realm, but quickly left when Kai spotted a mysterious figure stalking them. Unfortunately, the twins left behind their friend Saburo.

Kai returned to the mystic realm years later as a teenager and discovered that Saburo still existed there, not having aged a day since he was left behind. He learned that Saburo now served a red dragon named Lord Rinjin who was the mortal enemy of another being named Aratsu. Rinjin told Kai that if Toshi refused to submit to Aratsu's demands, he would have to leave her alone. Rinjin warned Kai to ensure that this happened or else there would be great trouble.

Their adventure in the mystic realm resulted in the resurrection of Kai and Toshi's mother. Though alive, she still suffered severe scars as a result of Aratsu's swords. Kai's mother was under observation at a local hospital, where she remained unconscious. Kai's grieving was interrupted by a gang of evil imps, which started to consume pieces of his mother's memory. They ran when Kai attacked them as they feared his touch, but soon found weapons in a part of the hospital that had been closed for renovation. He was saved by Nidoru, Goddess of Needles, appeared and saved Kai's life, dispatching the evil imps with ease.

Nidoru revealed that she was aware of the debt that Kai's father owed to Aratsu. She explained that the imps were attracted to his mother's soul, which was also cut apart by Aratsu's swords - shredded souls being easier to consume. She offered Kai a chance to save his mother's soul if he would assist her in defeating Aratsu. Kai agreed and his mother awakened too late to prevent him from making the deal with Nidoru.