Ningen(Nin, for short) is a Boss Monster, known for his incredibly fast magic attacks, as well as his Giant Killer's Kanabo( A kanabo is a powerful club-like weapon with the head covered in spikes), imbued with his water magic, which boosts its weight and Nin's strength. He's able to stop at least 6 armed humans, even armed with ranged weaponry.

His body is large and strong, perfect for wielding his weapon, but is more suited for the water. He wears special armor, appearing to be made of a magically-tempered white metal, made to amplify his weapon's magic, as well as his own, and to walk on land. He's a sibling of Undyne, but is often overshadowed by his big sister. He envies her emotional strength. He turned to being eperimented with a small dose of Determination, which mutated him, making his body grow to immense strength, weight, and height. His body became extremely strong and his digits grew webbing inbetween them. his head grew into his body giving him a fat appearance.