Turdak is a Tibetan lesser deity associated with illness and death. He is a servant of Yama and is depicted as a humanoid skeleton. While Turdak can bring illness and plague upon mankind, he also has the power to cure illness, or expel illness-causing demons if a dance is performed for him.
Turdak is also seen in Hindu mythology, where he is again the servant of Yama, judge of the dead. Turdak's role has changed, and he is considered an executioner of judged souls. After Yama has pulled a soul from a corpse and sentenced it to Hell, it is Turdak's job to haul that soul to the proper level of Hell.
"Origin: Tibet. The ruler of disease. He is Death. He appears as a skeleton, and brings about disease and death. He can also purify disease by dancing."
—Shin Megami Tensei A-Mode DDS Dictionary
Shin Megami Tensei IMAGINE
"A skull that serves his relative Yama, lord of the dead. He is viewed as the embodiment of disease, and often depicted as a skeleton. Turdak can bring disease and send people to their deaths, but he also has the power to cure disease by dancing. He is often described as a pair of beings, one that brings disease and one that cure it."
—Shin Megami Tensei IMAGINE Compendium
Turdak can be contracted in the bronze level of Ichigaya's Kagurazaka Zhu Que Caverns. He appears as a field boss in Ichigaya, a nightmare mob in the basement levels of Old Ichigaya Camp, and a regular mob in Ikebukuro's Zoushigiya Cemetary.
Devil Summoner: Raidou Kuzunoha vs The Soulless Army
"A Hindu executioner of judged souls, under the command of Yama, the god of death. When Yama passes his judgement, it is Turdak`s task to haul the soul to the proper hell."
—Devil Summoner Devil Chart
Persona Q: Shadow of the Labyrinth
Turdak can only be fused after getting the Scarlet Brace Key Item from completing the request, Time For a Warm-Up. The request involves fighting Elizabeth wielding Turdak as her Persona, and is available after reaching Group Date Cafe Stop 4.
