Like Shou, Kai is also part of Wingfield's royal lineage and able to open portals when his blood is combined with his brother's. According to the creator, he takes after his mother.

However, his upbringing was less normal. At the age of 5, Kai was separated from his brother and taken to the Wakabayshi research laboratory. He was part of a group of candidates for the role of heir to the Misonou Concern. While in the laboratory, he met Nagi, who was part of a different set of experiments.

One by one Kai watched all the other children disappear, until he was left all alone. He ultimately became Misonou's heir, but his father raised him never to apologize to anyone, to lie when it suited him, without any sort of real emotion.

When Kai was fifteen, his father fell ill, and Kai became acting chairman of the company. Then Wakabayashi came to him, and used a computer virus to blackmail him into attending Yuusei Gakuen.

The personality Kai puts forth makes him a natural seme. He is possessive and a little forceful. He also makes a very believable uke, as he is very confused and needs to be led when it comes to matters of the heart.