Atavaka ("lord of the forest" in Sanskrit), or Daigensui Myo-O (大元帥明王) in Japanese, used to be a child-eating demon until he received Buddha's enlightenment. He then became one of the Yaksha Kings and vassal to Bishamonten, as well as the protector god of the southwest.
Atavaka appears as the final boss of the Nakano Boundless Domain instance. Players can obtain the ability to fuse him in a special double-fusion by acquiring a rare object from the endchest there. He is a fusion of Hanuman and Yaksa.
Devil Summoner 2: Raidou Kuzunoha vs. King Abaddon
"The god of warfare and protection in Buddhist lore. Also called the Great General Myo-o. When Siddhartha died, he imparted the teachings of Buddha to the gods and made them swear to protect humanity."
—Gouma-Den Devil Chart
Atavaka appears as a boss in Chapter Three in the Great Summoner's Hall if Raidou is Neutral/Chaos-aligned. He inflicts fatal injuries on High Pixie during the fight against Nagi, which leads to her death after Raidou beats him.
Persona 3 FES
"Among the eight Yashaou, and one of Bishamonten`s attendants. Originally a child-eating demon, he was converted by the Buddha and became a protector figure."
—Persona 3 FES Compendium
Persona 4
"Among the eight Yashaou, and one of Bishamonten's attendants. Originally a child-eating demon, he was converted by the Buddha and became a protector figure."
Two Atavaka take part in a second ambush in the Karma Society Tower, after defeating the two Eligor enemies. Upon trying to question a surviving Karma Soldier the another group will shoot the survivor and transform into Atavaka to attack the party. The will later start appearing in normal encounters on the 20th floor.