Monokid is a child-like robot. However, he also has a very bad mouth and a short temper, and he's considered the hooligan of the group. He is a noisy and vulgar bully. He enjoys rock music and playing his guitar, and occasionally shouts exaggarated high-pitched screams like a rockstar. He also apparently loves eating salmon and especially honey, which for some reason can make him drunk.

He appears to be one of the more unintelligent Monokubs. He doesn't pay attention when others are talking and will randomly spout incoherent nonsense, making him the main cause of conversations getting derailed. He occasionally messes up words or says things backwards, and loves to shout his catchphrase "Hell yeah!"

Monokid is also most violent out of the siblings. He gets very excited about violence, claiming that it "turns him on". He also habitually bullies Monodam, even though they should be comrades, and seems to use any opportunity he gets to abuse him for the tiniest reasons or for no reason at all. It's said that this is the reason why Monodam has closed his heart.

Despite his general aggressiveness, he sometimes panics and shouts loudly and fearfully, like whenever his father is angry or at one point when Kaede confronts him. He also seemed to panic and yelled for Shuichi and Kaede to wait when they ran away from his Exisal, seemingly not expecting that to happen. He also tells Monophanie to shut up and threatens her with bullying when she calls him a dummy. All of this might imply that he is secretly insecure.