Tomah, operating under the aliases Tooma (トーマ) and Eraser-01 (イレイザー01), functions as an antagonist within the Xenon organization. He possesses brown hair reaching his neck and gray eyes, frequently wearing glasses and gloves. Introduced as a brainwashed Xenon agent codenamed Eraser-01, he pilots the Gyrozetter Guiltice, distinguished by shoulder-mounted blades and a later-acquired Moebius engine that grants autonomous function. His missions primarily target Arcadia Academy and its Gyrozetters, notably clashing with Kakeru Todoroki and Raibird in episodes such as "Appearance! Eraser-01!" and "Clash! Raibird vs. Guiltice!".

Combat-induced resonance between Guiltice's Moebius engine and Tomah triggers fragmented memories, weakening Xenon's control and leading to his defection. He reclaims his original identity as Souta Gunji (軍司ソウタ), one of the six Rosettagraph-prophesied chosen drivers. Reintegrating into Arcadia Academy, he pilots Guiltice against Xenon. His relationship with Kakeru shifts from adversarial to collaborative, culminating in a Double Burst attack merging Guiltice's ice with Raibird's fire.

A revelation in Episode 48 exposes Tomah's origin: he is a clone created by Xenon leader Goat, modeled after Goat's deceased son. This disclosure triggers profound identity conflict, particularly for Haruka, another clone modeled after Goat's daughter. Tomah's arc concludes with his participation in Arcadia's final battle against Xenon's Adamant Titan, solidifying his position among the chosen drivers.