Yo is a character from Street Fighter II V. He is an old master of Chinese martial arts and medicine.
Ryu meets Yo when it seems the latter is about to die, as he is sweating and looks to be in bad condition. Ryu says he will call an ambulance for him, but Yo insists on Ryu taking him to a place of privacy. There, Yo practices a martial arts technique in front of Ryu, where he uses his "chi" (or "ki") to create a blue fireball from his hands. He swallows this fireball, and, after it explodes in his stomach. Yo turns out to be fine and back in good health. Ryu wants to learn how to do the technique the old man just did, and so he takes him to his shop where they can have some privacy and practice the technique. Ryu doesn't master it, although he gains a little more knowledge about his spiritual self after this encounter.