Theseus fights as a boxer for Team Greece in the World Tournament story arc. He is one of five team members serving under leader Apollon, collectively representing the Twelve Olympic Gods within the narrative. As part of Team Greece, he competes against Team Japan in the Jr. World Championship. His match against Jun Kenzaki features high-stakes combat. Theseus employs a fighting style marked by acrobatic movements and sophisticated footwork, creating a dynamic presence in the ring. His signature technique is the "Aurora Thunderbolt," a powerful punch developed during training.

His most documented superblow is the "Heart Break Cannon." This technique delivers a devastating punch with pinpoint accuracy to the opponent's heart, combining precision targeting and immense concussive force. The impact lifts opponents off their feet, intending to slam them heart-first onto the ring's steel post to maximize trauma, carrying significant in-universe danger due to the risk of cardiac arrest. Against Kenzaki, he successfully lands the Heart Break Cannon, demonstrating its effectiveness and nearly securing victory.

His documented appearances are confined to the World Tournament arc. He also appears as a playable character representing Greece in the official "Ring ni Kakero" video game for the Super Famicom.