Is a chosen knight, protector of the diamond. He first comes off as rude and arrogant towards Himeno, but also has his nice side. He cares deeply for her and has feelings towards her as well. He rejected taking the knight ceremony because once accepting all the terms he will not be able to openly love Himeno, and if he does, death is the punishment. After she gets injured he does accept to go through with the ceremony to protect Himeno. He is a servant for the Mistuba's and is also Mamoru's half brother (same father). Keigo also attends the same school as Himeno.
He accepts Himeno's confession but cannot confess his love himself, but they stay together in the end without breaking the terms of the knighthood.