Isshin is the Gold Raiju Prime Nefilim, 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, he came to terms with it. 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 missions, as there's a dark history behind the motive. He was the only child in his family being raised by both of his parents until his mother, who is also a Rajiu Nefilim, disappeared at the age of 15, and his father, who was killed in a car accident at 18 during his trip to the United States. He later finds out that a yakuza member orchestrated it. Balancing two different lives, he's mostly determined to find his father's killer while also fulfilling his duty as the Raiju Nefilim in secret and in search of his mother.