Isshin is the Gold Raiju Modifer, the original primary color of the Raiju Clan, calling it the pure lightning wolf. To his knowledge, he was dumbstruck to find out that he was related to the Mark brothers but eventually, shook it up to nerve. He's cold and intimidating at times but is loyal and does whatever it takes to make sure the people closest to him are safe. There's a reason why he's strict on protecting people as there's a dark history behind the motive. He was the only child in his family being raised by his father until his wrongful death when Isshin was 18 years old during his trip to the United States. He later finds out that it was orchestrated by a yakuza member. Balancing two different lives, he's mostly determined to find his father's killer while also fulfilling his duty as the Raiju Modifier in secret.