The famous Japanese ghost story Banchou Sarayashiki tells of the love between an upper class samurai named Aoyama and a beautiful servant girl named Okiku. It is set in 1655, and many versions of this story have been written since the seventeenth century, sometimes Okiku returns Aoyama's love, other times she rejects him. One thing remains true throughout however, the couple's web of broken trust and promises ultimately leads to Aoyama killing Okiku, and casting her body down into a well. Her spirit then returns to haunt the grounds, either out of sorrow or anger.
In 1795, Japan suffered from an infestation of a type of worm that could be found in old wells that came to be named Okiku mushi. This worm, covered in a thick thread as if it were bound, was believed to be the reincarnation of Okiku. Since then, she has often been depicted as a beautiful girl with the body of a worm from the waist down, and her arms tied behind her back.
"An insect demon that takes the form of a woman with her hands tied behind her back. It arose from the hatred of a girl named Okiku, who was falsely convicted of a crime and executed. Note that this Okiku is different from the Okiku of the Bancho Sarayashiki, but they are often seen as the same person."
—Shin Megami Tensei: Strange Journey compendium
Shin Megami Tensei IV
"An insect demon that takes the form of a woman with her hands tied behind her back. It arose from the hatred of a girl named Okiku, who was falsely convicted of a crime and executed. She is a separate person from the Okiku of Bancho Sarayashiki fame, but because of its popularity, they eventually were seen as one and the same."
—Shin Megami Tensei IV profile
Okiku-Mushi can be found in Shinjuku National Park. She can teach Flynn the Poisma, Tathlum Shot and Mudoon skills through her Demon Whisper.
Shin Megami Tensei IV Apocalypse
Okiku-Mushi can be found in Shibuya. She can teach the Rakunda, Tathlum Shot, Poisma and Mudoon skills through her Demon Whisper. Okiku-Mushi gets a bonus to any Gun, Darkness, ailment and support skills learned.
Devil Summoner: Raidou Kuzunoha vs. The Soulless Army
"An insect demon that takes the form of a woman with her hands tied behind her back. It arose from the hatred of a girl named Okiku, who was falsely convicted of a crime and executed."
—Devil Summoner: Raidou Kuzunoha vs. The Soulless Army devil chart
Okiku-mushi is the final challenge that Raidou Kuzunoha the XIV faces in the Kuzunoha Training Hall. She states that she cannot be free until she has slain 100 devil summoners, and proceeds to ask Raidou if he will die for her before attacking. Okiku-mushi is weak to Fire, which Raidou must rely on Ukobach to take care of in this fight. Okiku-mushi will also summon Zombies to support her during the battle. After she is defeated, Okiku-mushi thanks Raidou before vanishing.
Okiku-mushi returns as a boss in the Matrix Labyrinth within the Daidouji Factory, guarding the Blue Shard, Red Shard and White Shard. They first appear as three normal enemies before large versions replace the weaker ones after they are defeated. These larger Okiku-mushi use Mudo in addition to their Marin Karin area of effect Mind/Charm skill. In the final encounter, there will immediately be a large Okiku-mushi accompanied by three smaller variants. More large variants will spawn in as the battle progresses and they will summon additional small Okiku-mushi during the battle.
Okiku-mushi also appears as a random encounter within the Matrix Labyrinth within the factory. Her Marin Karin skill inflicts Charm in a small area around her during combat, making getting close to her for too long treacherous, turning Raidou's demon's against him and potentially leaving him defenseless.