Gentaro Myodoin is the principal of Myoudouin Academy and head of the Myoudouin family's local dojo. He is grandfather to Itsuki Myoudouin and holds positions of authority within both the academy and the family's martial arts tradition. His appearance reflects a traditional elder, often shown wearing formal or martial arts attire befitting his status.

His personality blends strictness, patience, and wisdom. He emphasizes discipline in training and values self-discovery for his students and granddaughter. Despite a reserved and stern exterior, Gentaro prioritizes honesty and personal expression, especially concerning emotions or martial arts philosophy. He permits individuals to pursue their own interests, demonstrated by his support for Itsuki's engagement with fashion and cute aesthetics despite family martial arts expectations. His relationship with Itsuki combines familial affection with mentorship; he cares for her well-being and encourages her to follow her genuine path.

Within the family, he oversees the dojo and academy, ensuring the continuation of the Myoudouin legacy. Due to his son Satsuki Myoudouin's health issues preventing him from fulfilling heir duties, Itsuki temporarily assumes a cross-dressing role as the public heir. Gentaro accepts this arrangement while maintaining traditional expectations. His documented involvement centers on guiding the family and institution, without direct participation in primary conflicts involving the Desert Apostles or the Pretty Cure team.