Actor Allusion: Akira Kamiya, the original voice of Kenshiro, plays Ryuken. When Chibi!Kenshiro hits Ryuken's pressure point to make him younger, his face transforms into the original Kenshiro's design including the eyebrows.
Hey, It's That Voice!: To get the most notable out of the way, the original Kenshiro seiyuu himself, Akira Kamiya, voices Ryuken in this series. He even brings out his old Kenshiro voice for one comical segment.