Isa Miyoshi-nyudo forms one half of the Miyoshi brothers duo alongside Miyoshi Seikai within Sanada Yukimura's Sanada Jyuuyushi. Known as the Nyūdos Brothers, their shaven heads and status as nyūdō (Buddhist priests) reflect historical hints about the Miyoshi brothers. They consistently appear bald and wear sunglasses, following Yukimura's command to conceal their notably pretty eyes.

The brothers exhibit flawless synchronization in movement and combat, functioning as a single, unified fighting entity. This exceptional coordination allows them to unleash powerful combined techniques like "Nyuudous Punch," "Nyuudous Kick," and the "Nyuudous Special Attack." They possess superhuman physical capabilities—strength, speed, agility, and durability—complemented by mastery of ninjutsu and hand-to-hand combat. Crucially, they can merge their bodies during battle to execute these devastating joint assaults.

Assigned to protect Sakuya within the Red Tower, they initially present themselves as a single Nyudo figure guarding the location. Their role consistently emphasizes their function as elite defenders and loyal retainers integrated into Yukimura's forces. Isa Miyoshi-nyudo's depiction remains inseparable from his brother Seikai, focusing exclusively on their paired combat effectiveness and unwavering service to the Sanada clan.