Kouji is a student at Rosewood Private School (known in the Japanese version as Seidou Gakuen, "Bronze Institute"). He comes from an extremely wealthy family and is often somewhat spoiled and prideful. A highly skilled Medafighter, Kouji and his Medarot Sumilidon are renowned for their undefeated record in Robattles.

Kouji and Ikki are rivals, though they are able to coexist largely due to their mutual feelings for Karin. Kouji is convinced that he is Karin's boyfriend and frequently trains with Sumilidon in an effort to master the Shadow Sword technique, taught to them by Space Medafighter X.

He has a strong fear of insects, stemming from a childhood incident where he collected a mantis egg sack and forgot about it, resulting in it hatching and frightening him. This phobia extends to Medarots like Spidar, which he openly fears, though he does not seem to react similarly to Metabee despite its insect-like design.

Alongside Ikki and Space Medafighter X, Kouji represents Team Japan in the World Robattle Tournament.