Ryo is the best duelist in Duel Academy. Unlike his little brother (Sho Marufuji) he excels in all dueling forms. He often studies the dueling format with all duelists, and never underestimating his opponent. He uses some of the most powerful Machine Type monsters in the game, that's why he's called the "Kaiser".
In the manga, Ryo is an exchange student to the U.S who returns to Duel Academy with two attendants.