Kai von Granzreich is the second prince of the Kingdom of Granzreich.
Kai is a tall, large young man with short hair swept over his left eye.
Initially, the color of his hair was brown, but this seemed to have changed recently to an ash-blond color. Like the rest of his family, he has blue eyes. He has broad shoulders and is the strongest of his siblings. His naturally sharp eyes make him seem like he's always glaring even though he's not.
- Anime: his hair was a whiter platinum blond.
Despite his frightful appearance, he is the most kindhearted of his siblings. He loves touching soft things and is very warm and gentle, but is very bad at talking. Because of his appearance and difficulty speaking, Kai is feared by the castle staff, but his siblings and Heine are aware of his gentle side. Though normally calm, he can be enraged when someone hurts those he loves, proving him to be protective and loyal to those he cares for. He is fond of Heine because he is the first tutor to speak properly to him and not be afraid of him, and also because Heine is small and cute, which Kai loves. Kai loves fluffy soft cute things but will only pet living things and while somewhat fond of non living soft things, he does not like petting them nearly as much. In terms of romance, he is rather dense as evidenced by his obliviousness towards his fiancee's (Beatrix's) attempts at winning his heart. He is an animal and flower lover, often making rings of flowers for his sister and Heine. In fact, animals tend to flock around him. In addition, despite being slow at speech, he is actually very intelligent with his average scores being around 87. He also has surprisingly fast reflexes, once managing to catch a robber while everyone's attention was on the victim. He acts as the mediator between his siblings when they fight, as he hates it when his family don't get along since he loves them dearly. He is extremely pure and naive, preferring to be a king who brings peace and acting the most innocently. His brothers remarked they can't fight back when he intermediates because he is so pure and naive. He is rather lazy, preferring to laze around in the garden and take naps while finding simple things like dressing and getting up annoying, but he loves to eat. He also feels that because people judge him for his looks and are so afraid he should not try to correct the misunderstanding because he fears he would only scare them more, though Heine reassures him that he must take the first step so people can get to know him better. While Leonard is good at sports, it is demonstrated that Kai is also extremely sporty, once managing to carry a heavy statue with little effort (causing his brothers to call him a monster of his own). In addition, he caught a thief quickly and managed to catch up to a moving carriage to tell Beatrix thanks for a picnic she organized. He tends to be carefree, airheaded and in another world but his kindness, maturity and gentle nature make him well loved by his loved ones. Of his bothers, he and Licht act the least like royalty, with the two being perfectly fine doing "commoner things" like eating without a fork or knife and having a picnic lying on the grass and not sitting on the table. On a side note, he loves drawing but is a terrible painter, drawing an abstract painting that didn't resemble his model in the slightest (it looked like a Picasso style bird when he was supposed to be painting his dog).
Kai was engaged to his cousin Beatrix at a young age. When he was fifteen, he was sent to the military academy, as per the royal family tradition. Bruno joined him later, but was bullied by Ralf von Fuchs. When Kai found out, he went into a rage and beat him up, causing them both to be expelled from the academy.