A young man who finds Atsuki sleeping in the snow one day, tired out from preparing for high school entrance exams. Despite his illness keeping him from attending school, Kai is quite intelligent and resolves to tutor Atsuki, growing closer to her in the process. He promises to meet her at the school the day Atsuki finds out the exam results, but never shows up.
Atsuki learns later that Kai's illness was more serious than he let on, and his absence was only due to his untimely death. Beforehand, he asked Takami, his younger brother, to take care of Atsuki if the worst should happen.