Koumokuten (広目天), also known as Virūpākṣa in Sanskrit, is the guardian deity that protects the west of Buddha's realm. His name means "vast/all-seeing eyes." He has red skin and leads the troop of Nagas, the lesser snake-man gods. Some statues have him carry a Pasha which works similar to a lasso for capturing running target. Many of his attributes are very similar to Varuna, who happens to be the guardian of the west in Lokapala.
"Origin: India. One of the 4 Heavenly Kings in Buddhism. He protects Mt. Meru's west and Aparagodaniya with a trident. He is also known as the king of the Naga. He can see all, and has the power to punish evildoers and reform them."
"As a Defender of Law, Koumokuten is considered one of the Four Heavenly Kings featured in Buddhism. He holds a three-bladed vajra and has been assigned by Lord Sakra with protecting the western domains of Mount Neru. He has strong ties with the Naga, and is sometimes depicted as being their king. He is said to be omniscient, a power he uses to find evil deeds being committed all around the world and redirect these sinners towards the path of righteousness."
—Shin Megami Tensei IMAGINE Compendium
Koumokuten can appear alongside the other kings in Ichigaya Camp's gold-level instance by defeating the Pisaca mini-boss on the basement floors.
Koumokuten is faced in the Challenge QuestTokyo Cosmo. He is found in the Nakano area of the Shinjuku Region. He appears alongside the other three once all four have been defeated to be fought as a group. Koumokuten mentions after the Four's final defeat that Flynn is the only one to defeat them without the Orb of the Four Gates breaking.
"Koumokuten, or Virupaksha, is one of the Four Heavenly Kings in Buddhist lore. He dwells halfway up Mt. Meru in the center of the world and protects the West under the command of Sakra. He keeps a close watch on the world with his sharp gaze and enlightens people with his speeches. He is commonly depicted wearing armor, with a trident in hand and an angry expression on his face."
—Shin Megami Tensei IV Apocalypse compendium
Koumokuten and the rest of the Four Heavenly Kings guard the temples that contain the jars of Aether which maintain the Tokugawa Mandala for the Divine Powers. Koumokuten can be found in the Hakujoin Temple, guarding the jar of Aether which contains the essence of Gluttony. Defeating Koumokuten will unlock him for fusion in the Cathedral of Shadows.
Koumokuten can teach Nanashi the Ziodyne, Mortal Jihad, Sukukaja and Titanomachia skills through his Demon Whisper. He benefits from learning Physical, Electricity and support skills.
Koumokuten (named Koumoku due to character space limit) is one of the four Devas that protect the barrier between the demon and human worlds. On every ending save for Yuzu's, in order to gain access to the demon world (and thus, Babel) the player's party needs to dismantle the barrier that the Devas protect. After Bishamon's defeat, Koumoku challenges the player's party with Zouchou, planning to make up their lack of power with numbers.
Koumoku and Zouchou are unlocked for fusion after the player defeats them.
"Koumokuten, or Virupaksha, is one of the Four Heavenly Kings in Buddhist lore. He dwells halfway up Mt. Meru in the center of the world and protects the West under the command of Sakra. He keeps a close watch on the world with his sharp gaze and enlightens people with his speeches. He is commonly depicted wearing armor, with an trident in hand and an angry expression on his face."
Koumokuten's design which is borrowed directly from Tōdai-ji has him carries a writing brush and a scroll instead of any conventional weapon which indicate his focus on literature among the Four Heaveny Kings.