Yoriichi - The legendary demon Slayer and the creator of Sun breathing aka the original breathing style. He weilded his crimson blade striking fear into demons like nothing and destroying them with pure skills and menacing aura as of his feats of defeating muzan in seconds 

Muzan Kibutsuji - the demon king and creator of the demon race, he is the one who had created the 12 Kizukis. He has a lot of advance biological capabilities and very much high IQ and is a dengerous apex predator