Yoshioka Kenpo was renowned for his skills with the sword and became the official instructor of the shōgun Ashikaga Yoshiharu (reigned from 1521–1545) in Kyoto.
Since the usage of weapons of any kind was strictly forbidden at the court on pain of death, Kenpo was declared a criminal and pursued.
Nonetheless, Yoshioka Kenpo had built the foundation for one of the most famous Kenjutsu ryū (sword fighting styles) of Kyoto, led by his children and grandchildren.
Musashi had sought them out as a way to leapfrog his way to fame, slaying a few disciples at the dōjō before Seijūrō arrived and exposed him as lacking.
At the duel, Musashi was delayed by Ryōhei threatening him with revenge should he win but had so advanced as a swordsman as to defeat Denshichirō fairly and with relative ease, killing the second brother at Rengeoin temple.
(There is no third biological brother in Vagabond, where Ueda Ryōhei had been adopted by one of Kenpo's disciples, and even before Denshichirō's death he had the support of at least a sizable number of the Yoshioka swordsmen.)