Kosma is a young boy who joins the MOTHs to become a hero that protects people one day. He is very reserved and distant, he speaks little whenever he feels like it. He overthinks a lot and is uncertain how to keep a conversation on so he remains quiet all the time. He is self-conscious about finding the right words, he comes out harshly by accident when trying to speak. Kosma likes children and dotes Griseo like his own sibling, looking after her in her dad's stead, Ato.