Geppei Okaki is a human teenager with black hair cut to ear length and green eyes. He initially exhibits a selfish and stubborn personality, particularly concerning ownership of a hidden garden patch he believes is his, though it was actually associated with a cat named Torte years earlier. This possessiveness sparks conflict when he encounters Kinako Monaka and Taruto in the garden, resulting in a rivalry with Kinako. His character develops considerably over time. Geppei transitions from being mean-spirited and possessive to growing into a caring, generous, empathetic, moral, lenient, docile, and supportive individual. This transformation occurs as he resolves his differences with Kinako; they evolve from rivals into close friends who frequently embark on adventures together. He demonstrates strong loyalty to his friends, disliking being alone or losing anyone within his group. Geppei owns a pet cat named Gallette, one of the few cat boys depicted, who accompanies him everywhere. His likes include hiking with Kinako and winning, while his dislikes center around losing and separation from others. A possible romantic interest in Kinako is hinted at.