Tommy, whose full name is Tomisaburo Tengai and who is also called Tomi, is Shinichi Kuruma's close friend and the brother of Maria Tengai. He possesses extrasensory perception, though his abilities are consistently weaker than his sister's. Following Maria's death—significant to both Tommy and Shinichi—Tommy becomes involved in Shinichi's conflict against Genzou Kuruma.

He joins Shinichi and Ayaka Sanders in their efforts to evade Genzou Kuruma and his genetically altered followers, the "New Humans." Unlike Shinichi and many adversaries, Tommy cannot transform into a monster or summon creatures. His role centers on providing support and assistance to Shinichi and Ayaka during their escape and confrontations, operating as a dependable ally within the constraints of being an ordinary human facing extraordinary threats.

His motivation stems from his relationships, particularly his loyalty to Shinichi and the legacy of his sister Maria. Before her death, Maria Tengai was uniquely destined to awaken God. Her final wish involved Shinichi, and her consciousness later manifests through Ayaka Sanders due to the purified blood cells from Shinichi that Ayaka carries, adding emotional complexity to Tommy's interactions with Ayaka.

Tommy's established traits—human vulnerability, loyalty, and supportive friendship—remain consistent throughout the narrative, with no substantial character development, evolution, or expanded background documented in the series or any official additional media.