Tomisaburou Tengai possesses psychic precognition, a power he and his family employ for survival through street-side predictions after fleeing their village's destruction by the 13 Apostles, led by Dr. Genzou Kuruma, an event that claimed their parents' lives. He roams with his sister Maria and their grandfather. Shinichi Kuruma first encounters them when rescuing the family from gangsters, subsequently seeking their aid to locate and eliminate the Apostles, scientists responsible for horrific human-animal fusion experiments. Tengai's grandfather fears Shinichi may embody a prophesied beast destined to bring about the apocalypse through his vengeful quest.

Tengai's precognitive abilities prove critical throughout, providing vital warnings of impending threats. He cautions Shinichi that association with Ayaka Sanders—a girl psychically linked to him via cells derived from his blood—risks tragedy, mirroring the earlier fate of his sister Maria. Maria, believed a reincarnation of the Virgin Mary, was killed by the Apostles, an act that triggered the catastrophic "Great Destruction" earthquakes. Tengai evolves into a steadfast ally to Shinichi, actively aiding in battles against the Apostles' monstrous creations, the Newmen or Demonic Beasts. His motivations remain deeply rooted in avenging his slain family and preventing further catastrophes ignited by the Apostles' actions.