Kōketsu was a samurai lord who mentored Izou during the civil war before the Meiji Restoration. He betrayed Izou in the conflict, an act that cost Izou his right eye and ended his samurai status, cementing Kōketsu as Izou's sworn enemy.

After the war, Kōketsu ascended to become a high-ranking officer within the Inferni faction. This organization pursued magical artifacts to awaken a mythical Dark Lord and plunge the world into eternal darkness. Commanding subordinates, including an unnamed human leader directing assaults on elves, Kōketsu operated from a Yokohama manor. There, he negotiated with figures like Ōkubo Toshimichi, offering Inferni membership in exchange for securing a specific magical wand.

Kōketsu's primary goal focused on capturing the young elf Sonya, bearer of a hereditary magical wand possessing immense power. He masterminded the assault on the Kyoto brothel housing Sonya, spearheading the operation to seize both her and the wand. This attack resulted in the death of Chihaya, Sonya's protector.

In the climax, Kōketsu personally captured Sonya and transported her towards Inferni's stronghold. Aboard a ship, he confronted Izou for their final battle. Gaining the upper hand, Kōketsu blinded Izou's remaining eye and stabbed him. Before he could finish, Sonya unleashed the wand's full power, casting a spell that disintegrated Kōketsu into dust.