Lock Keepers are special Shadows that ward off intruders from the "Bird Cage," or a part of the Jail that locks its Monarch within. Their purpose is not to keep intruders out, but to lock the Monarch within their traumas and prevent them from returning to their weak selves by constantly reminding them of their traumatic experiences, thus encouraging them to bask in their distortions. The area where the Lock Keeper resides is known as a "Trauma Cell," and is rooted in the real-world location where the Monarch's trauma took place. When entered via the Metaverse Navigator, the Trauma Cell will take the form of a recording of said trauma, complete with the Lock Keeper taking the form of the person who traumatized the Monarch, but with hollow black eyes. Once an intruder is spotted, the Lock Keeper will be provoked and transform into a massive, black humanoid with horns and four arms, each holding weapons that vary between each Lock Keeper. Weaker Shadows, including Persona counterparts, accompany the Lock Keeper. Defeating this Lock Keeper will break the barricade to the Jail's cage, and the Phantom Thieves usually send a calling card to the Monarch after this. The Monarch will snap and attack the Phantom Thieves once they enter the Jail after sending a Calling Card and must be defeated to free all of the Monarch's worshipers as well.
All Lock Keepers are weak to Bless and Curse, usually having weaknesses to elements that the Monarch is weak to as well.
Shibuya Jail: The Lock Keeper takes the form of a girl bullying a young Alice Hiiragi by stomping on her and taking photographs of it. When attacking, it wields large axes in each hand. It has additional weaknesses to Fire and Wind.
Sendai Jail: The Lock Keeper takes the form of a man who was Ango Natsume's publisher. He was discussing with another fellow publisher about fleecing Natsume using his grandfather's name and criticizing Natsume's book as incoherent and dull, while being eavesdropped by Natsume. When attacking, it wields swords in each of its hands. It has an additional weakness to Ice.
Sapporo Jail: The Lock Keeper takes the form of a corrupt senator who was discussing with a sponsor about usurping Mariko Hyodo's seat as Mayor by manipulating a snow sculpture accident that killed a 7 year old child. Hyodo was eavesdropping on the discussion and threatened to call the police, only for the senator to remind her that reporting the incident would lead to her immediate removal, as Mariko was technically responsible. When attacking, it wields a shield in each of its hands. It has an additional weakness to Psy.
Okinawa Jail: EMMA summons this Lock Keeper to drive away intruders to the Okinawa Jail after a voice resembling Sophia's calls her out as a reject. This one has no weapons and floats in the air, although it can manifest weapons wielded by the previous three to attack or protect itself. It lacks any weaknesses other than Bless and Curse. The same type of Lock Keeper is also summoned by the Keter orb during the fight against Demiurge.
Osaka Jail: Takes the form of Akira Konoe's father, who attempted to kill young Konoe, only for Konoe to kill him in retaliation. When attacking, it wields bazookas in each of its arms. It has additional weaknesses to Elec and Nuke.