Masanori Iseki presents as a theatrical Buddhist monk with a shaved head, perpetually wearing black sunglasses. His eccentric style consistently pairs a black suit, pink undershirt, and tie, even in settings like hot springs. Earlier, during monastic training, he wore traditional robes but kept the sunglasses. His training in China led him to Tohya Ebata, whom he witnessed defeat several monks; impressed by Tohya's strength and ideology, Masanori became his partner.

Beneath this supportive facade lies a manipulative schemer. Masanori secretly exploited Tohya as a pawn in Team Daybreak's campaign to monopolize Vanguard in Japan by destroying rival teams through banner burning. He employed calculated lies about his intentions and backstory to gain sympathy or proximity to targets, exemplified by deliberately losing a cardfight against Zakusa to gather intelligence on Team Blackout and facilitate Tohya's attack.

Demonstrating his lack of genuine attachment, Masanori abandoned Tohya after his defeat and nomination to lead Team Blackout. He expanded Team Daybreak's influence under Mirei Minae's advisory but later deserted the team when their plans failed. His allegiance then shifted to the Uniformers project under Jinki Mukae, recruiting powerful cardfighters through extremist methods. Masanori ultimately admitted his primary motivation is personal amusement derived from corrupting others and witnessing their downfall, viewing organizations like Uniformers merely as tools.

Chosen as one of six participants in the Fated Clash after obtaining the Fated One of Taboo card, Masanori stated his wish was to cause chaos. However, he genuinely sought to resurrect Shingi Mukae from the dead—an impossible goal without the Clash's power. A decade before the Clash, Masanori attended a Kiyokura Group summer camp, interacting with other future participants including Akina Myodo, Hikari, Suo, Nao, Mikoto, and Taizo; these connections were forgotten over time. During the Clash, he displayed minimal animosity after elimination, despite discomfort around Suo.

Masanori later returned as a participant in the Deluxe tournament arc. His cardfighting style utilizes the Stoicheia nation's Regrain series, featuring necromancers practicing forbidden black magic—a contrast to his monk identity he calls a "beautiful contradiction" reflecting his deceptive nature. This deck's theme of manipulating the dead parallels his tendency to exploit others while maintaining a facade of subservience.

Throughout his appearances, Masanori exhibits a fascination with observing human behavior and provoking others to reveal their darkest traits, considering this his method of uncovering true nature. He maintains a curious and expectant attitude toward supernatural phenomena like the Masques cards, Griphogila, and the Fated Clash, aligning with his pattern of seeking out and instigating conflict for personal gratification.