Hekiji Tengai transitioned from devout Buddhist monk to Shie Hassaikai yakuza member after Kai Chisaki personally recruited him. Chisaki specifically enlisted Tengai to manage fellow Eight Bullets member Kendo Rappa, whose aggressive impulses and relentless pursuit of combat disrupted operations. As the newest Eight Bullets recruit, Tengai served as Rappa's handler, enforcing Overhaul's directives during missions. This career shift implied a profound personal transformation, potentially triggered by an undisclosed event that led Tengai to abandon monastic life and pledge absolute loyalty to Chisaki—whom he addressed reverently as "Master Overhaul." Tengai exhibited a calm, analytical composure rooted in his monastic discipline. He condemned combat as a "selfish desire," expressing disdain for prolonged violence while prioritizing swift resolutions. Despite these pacifistic principles, he enforced unwavering obedience to Overhaul's authority and corrected any perceived disrespect toward his leader. His dynamic with Rappa remained fraught; Rappa routinely ignored Tengai's tactical guidance and assaulted him mid-operation. Tengai tolerated these outbursts while maintaining focus on mission efficiency. His Quirk, Barrier, generated dome-shaped force fields of adjustable size around himself or allies. These barriers demonstrated steel-like durability against heavy impacts but fractured under sustained pressure or overwhelming force—such as Fat Gum's energy-absorbing counterstrikes. A key limitation prevented attacks originating from within the barrier. Tengai deployed this power strategically, synergizing with Rappa's offensive assaults to create a "spear and shield" partnership. During the Shie Hassaikai raid, his barriers intercepted attacks from heroes Fat Gum and Eijiro Kirishima until Kirishima's tenacity enabled Fat Gum to shatter the defense. After Fat Gum incapacitated Tengai and Rappa, Rappa disobeyed Overhaul by permitting heroes to secure medical supplies. Tengai protested this insubordination, prompting Rappa to physically overpower and knock him unconscious. Tengai was subsequently arrested and imprisoned with other syndicate members. His tactical acumen—observing enemy vulnerabilities and combat patterns—persisted throughout these events, though his narrative trajectory concluded without further development post-capture. His documented capabilities included power ranked 3/6 ("C"), speed 2/6 ("D"), technique 4/6 ("B"), wits 4/6 ("B"), and a "Rappa's Babysitter" role score of 4/6 ("B").