Monodam is a child-like robot. Unlike his overly talkative siblings, he is very quiet. For the most part, he doesn't speak even to his fellow siblings, and he is somewhat of an outcast in the group.

When he does talk, Monodam speaks in a typical monotone robotic manner, making him appear very emotionless and thus unpredictable. He tends to silently stare at others, with no visible reaction when others speak to him. He occasionally speaks short sentences unexpectedly in a rather loud voice, which may startle others due to his usual silence. The rare moments when he laughs sounds especially unnatural due to his very robotic voice. All of this causes him to come across rather creepy, much more so than his siblings.

Monodam is constantly bullied by Monokid, both verbally and physically, possibly because of his different looks. Monokid has fun making up new ways to be cruel towards Monodam and he also tends to blame Monodam for anything that goes wrong. This is said to be the reason why Monodam has closed his heart long ago. He appears to protest very little against the abuse he endures.