Oninaki is a 2019 action role-playing game developed by Tokyo RPG Factory and published by Square Enix for the Nintendo Switch, PlayStation 4 and Windows. Gameplay has players exploring dungeon areas selected from a world map, fighting enemies in real-time combat with spirit weapons called Daemons while shifting between the worlds of the living and the dead. Oninaki is set in a world where the doctrine of reincarnation is enforced by figures called Watchers, who assist in the passing of souls and fight monsters born of regret. The player controls the Watcher Kagachi as he confronts a shrouded figure called the Night Devil, uncovering hidden truths surrounding the cycle of reincarnation and his own past life.

Concept work began in 2017 during the last stages of Lost Sphear's development. Takashi Tokita, noted for his work on Chrono Trigger, came on board as a creative producer and pushed writer Hirotaka Inaba's story in a darker direction than his earlier work. The gameplay and graphics were also changed, becoming more action-focused and cinematic. The music was composed by Shunsuke Tsuchiya and Mariam Abounnasr of Procyon Studio. The game has received mixed reviews from critics upon release, with praise going to its mature setting and art design, though several criticised its story delivery and gameplay. It was the last game produced by Tokyo RPG Factory before its closure in 2024.

Oninaki is an action role-playing game where players take on the role of the Watcher Kagachi, who battles monsters called the Fallen while exploring the game world through two planes; the Living World and the afterlife world known as the "Beyond". Players view environments from an isometric angle, with Kagachi exploring dungeon environments completing both story-based and optional quests. Standard enemies roam the dungeon environments, attacking Kagachi on sight, while many areas end with a boss encounter.

During exploration and combat, Kagachi can find Healing Salves which restore health, upgrade artifacts, and grant new weapons. During combat in the Beyond, Kagachi gives and takes more damage. In the Beyond, the environment shifts, allowing for new routes to open or allowing access to teleport points for travelling between different areas. Players must explore both worlds in order to progress through the game, with areas that must be first explored in the world of the living, otherwise Kagachi must navigate a black void in the Beyond and can be killed in one hit by enemies. By defeating Fallen, Kagachi earns experience points which raise his basic statistics.

Kagachi battles the Fallen using Daemons, spirits manifesting as weapons. Starting off with a basic sword Daemon, Kagachi gains more Daemons as the story progresses. Each Daemon comes with a different weapon type, such as scythes, axes and spears. Daemons have different weapon-based skills, mapped to four different control buttons, each with a cooldown timer after use. Using a Daemon increases an affinity meter; reaching 100% raises Kagachi's attack power, while going above 150% begins decreasing his defence. When at 100% and above, Kagachi can trigger an empowered state. Using a Daemon in combat earns Soul Stones which unlock that Daemon's skill tree; unlocks include new combat abilities which are equipped to three of the four buttons, stat increases, and small cutscenes related to the Daemon's narrative. Using skills repeatedly unlocks bonuses for that attack. New weapons found during exploration and combat can be equipped to Daemons, with these weapons having slots for upgrade gems, which increase weapons stats.

Kagachi is a Watcher, a person charged with defending the Cycle of Reincarnation, killing monsters formed from regret with spirit weapons called Daemons and helping spirits pass into their next life by any means necessary. Kagachi works closely with both Kushi, his adopted father, and Mayura, Kushi's daughter, operating from the world's only city Szaka. In the aftermath of a mission against a cult rebelling against the Cycle of Reincarnation, Kagachi meets a girl who does not remember who she is, and so he names her Linne. She is being hunted by the Night Devil, a powerful spirit who hounds Kagachi and gives aid to the cult in undermining the current monarch Lobelia. Lobelia and her son Leo instruct the Watchers to focus on destroying the cult over their other duties, causing friction within the Watchers. During one mission against the cult, Mayura is killed and Kagachi helps free her spirit. The Night Devil confronts Kagachi several times, possessing Watchers with his hatred and eventually using Kushi as his host.

Kushi incites a rebellion, with the people demanding spiritual equality with the elite surrounding Lobelia. Kagachi tries to reason with the mob, but they attack and force him to kill them. As Kagachi confronts Lobelia, Kushi appears and reveals that Lobelia usurped the throne after having the last true sovereign Sara executed. Kushi attacks, but Leo protects Lobelia at the cost of his life. Kagachi then defeats Kushi, learning as he dies that the Night Devil is a Daemon filled with hatred that wants to end the world. Lobelia further reveals that the true sovereign was key to preserving the world, and a terrible force has been preparing itself since she ended the bloodline. Kagachi finds the Night Devil: Kagachi then learns that the Night Devil is a fragment of Kagachi from a previous life when Kagachi was named Soju, the banished brother of the true sovereign. After defeating the Night Devil and absorbing him, Kagachi kills himself to quell his hatred. Linne, transforming into an adult form, prays for Kagachi to make a new future as a monster emerges from underground to destroy the world.

Awakening as Soju in the past, Kagachi pieces together his history; raised by an assassin's guild, Soju acted as a precursor to the Watchers as he carried out the last wishes of lingering spirits. After one such mission, he was killed. Meeting Sara, he realises that "Linne" was her spirit. Sara explains that the sovereign must keep the Oni, a manifestation of the despair humans discard during reincarnation, from awakening; the monster seen awakening in Kagachi's last life was the Oni. They go to the First Pillar, an ancient magical landmark, and view murals of humans defeating the Oni and Sara's ancestress establishing Szaka, with the Oni sleeping under it. Journeying into the palace and entering the pool of despair at its heart, Kagachi experiences the hopes of those who fought the Oni in ancient times as he escapes; during this time he sees Szaka, called here the Wailing Land where the Oni sleeps.