Sekishūsai Tatewaki

Sekishūsai Tatewaki (帯刀 石舟祭 Tatewaki Sekishūsai) is Isami Tatewaki's grandfather and the sensei of a kendo dojo in Tokyo.

"Triple Combination! Swordbot - Samurai!"
Sekishūsai watched a bout between Isami and another of the dojo's students, where Isami was victorious. To remind his grandson that an enemy could strike at any time, Sekishūsai attacked him and challenged him to a bout. Before their duel could commence, they knelt before their family's sacred mirror. During their moment of silence, the Predacons Budora and Gaidora attacked, seeking the mirror, which was in actuality a Legendisc. To protect the "mirror", Sekishūsai ordered Isami to take it and flee, which the boy promptly did.

"The Invincible Swordsman - Ryōma Sakamoto!?"
While later practicing with Isami, Sekishūsai observed that his grandson had grown stronger, but Isami admitted that it was down to the power of the Legendisc he wore around his neck and thus it wasn't him growing strong. Sekishūsai told him that it was all right so long as he knew where the power came from, and that true power was having a strong heart.