He is Blood's shy younger brother who gets bullied for having pink hair. Blood had hope that after getting a position at The Cells he would be able to see Kaze live a normal life and watch him grow up and make friends, but instead Kaze spends most of his time being a shut in because when he leaves the house people make fun of his pink hair. Jolt a boy who is little younger than him is one of the few people who doesn't make fun of him for his hair, so he comes over often to hang out with him and tell them what they learned on class that day, and in return Kaze helps him with his homework, because despite being a shut in he still has the best grades in his class.
For more info on his backstory check out Blood Stream's backstory.