He is the younger twin-brother of KISHIMOTO Masashi (creator of Naruto). The two have been drawing manga together since early childhood, thus their styles are similar. As a result, the two have frequently been accused of copying the other. Seishi, himself, notes that the similarities are not intentional since they were both influenced by many of the same things while the more famous Masashi even asked fans stop calling Seishi a "copy cat." Seishi created the manga 666 Satan, which is serialized in Japan by Monthly Shonen Gangan and licensed by VIZ in America as "O-Parts Hunter."