Kai Miyagusuku

Kai is Saya's older foster brother. He is a talented athlete and baseball player and was very popular at school. He is very protective of his family, and he believes that because he is the eldest it is his responsibility to protect Saya and his younger brother Riku. This leads to conflict early on in the series as he finds it hard to accept that Saya is stronger than him and convinces himself that if Saya is in danger he has to save her. This causes David great annoyance, in particular, as he initially sees Kai as a distraction to Saya's mission. When his father dies Kai takes it very hard, but being the big brother figure that he is, tries to be strong so he can help Saya and more importantly Riku deal with it.

Kai is a bit of a hothead and is very impetuous. He is not accustomed to taking orders and being told what to do. This is never more evident as when David leaves him and Riku behind after George’s death, for their own protection. Kai will not accept that he is being left out and still believes Saya needs him and tracks them down.

As the series progresses, the many tragedies the party encounters force Kai to grow up rather quickly. Having initially seen him as an annoyance, David takes Kai under his wing and helps to train him to fight Chiropteran, and the two men become quite close in later episodes. David becomes like a father figure and when David is kidnapped Kai goes on a one man mission to rescue him.

Throughout the series he is also greatly annoyed by Hagi, as Kai cannot understand why Hagi blindly obeys Saya without ever expressing his own view and feelings.

Steadfast and Loyal, Kai resolves to stand beside Saya no matter what happens, and even though she does not need protecting anymore, he supports her unequivocally till the end.