In some episodes throughout the series, if you look hard enough, you will be able to see Akuma, another Street Fighter character.
Although the series depicts most of the cast of characters from various versions of the Street Fighter II video games, the only ones not featured are E. Honda, Blanka, Dee Jay, and T. Hawk.
The stance taught to Ryu by Master Yo Sen-Ko is actually the "San Ti Shi" stance taught in Xingyiquan.