This is the first game ever made to feature both SNK-established characters and the characters from the small, now bankrupt company ADK (responsible for the obscure and hardly popular "World Heroes" series) in the same game.
While bearing the name Mr. Karate, the character is actually Ryo Sakazaki, who bears the name and an older appearance in an obscure SNK fighter called Buriki One (his profile on the official site confirms this).
Robert's design is also original (his profile doesn't list his game of origin) to this game, and it is speculated that he is about 10 years older to coincide with Ryo's appearance in Buriki One (which was said to have been 10 years ahead of the current King of Fighters and Art of Fighting timelines).
Yuuki and Ai are the Japanese words for Courage and Love (respectively).