Shou Marufuji is a former Slifer Red, then Ra Yellow, and now Obelisk Blue (briefly in season 3, but permanently in season 4) student as well as Juudai's best friend. A decent Duelist, although hindered by a great deal of self-doubt, though this mainly stems from his brother Ryou's treatment of him, Shou' journey towards strengthening himself provides sharp contrast to the protagonist Juudai's active determination.