Complex sentence: He ultimately accepts his loss as a sign of good sportsmanship, realizing his error however, leading to the Great Leader using him to activate Rider Robo to attack the surviving Kamen Riders and those who defied Shocker.
Split into simpler sentences: He ultimately accepts his loss as a sign of good sportsmanship, realizing his error. However, the Great Leader uses him to activate Rider Robo to attack the surviving Kamen Riders and those who defied Shocker.