Oni (no relation)

With the popularity of the Japanese mythical oni, there are a number of works and characters titled "Oni". Despite the confusion this sometimes causes with Bungie's game Oni, due to the shared inspiration, interesting similarities can sometimes be found.

ONI RPG series and OVA

File:Misao and Akihito transformed.jpg

File:Misao and Akihito normal.jpg

In the OVA, Shuramaru meets two characters who can transform into oni like he can.

A classic RPG series created by Pandora Box, and once popular in Japan, depicted transforming heroes with beast forms.

GB	1990-12-08	鬼忍降魔録 ONI	Oni Shinobu Ko Ma Roku ONI
GB	1992-02-28	ONI II 隠忍伝説	ONI II In'nin Densetsu (cartridge photo)
GB	1993-02-23	ONI III 黒の破壊神	ONI III Kuro no Hakai-shin
GB	1994-03-11	ONI IV 鬼神の血族	ONI IV Kishin no Ketsuzoku
SNES	1994-08-05	鬼神降臨伝ONI	Oni Kishin Korin-den ONI
GB	1995-03-24	ONI V 隠忍を継ぐ者	ONI V In-nin o Tsugu Mono
SNES	1996-02-02	幕末降臨伝ONI	Bakumatsu Korin-den ONI
PS1	2001-03-22	ONI零〜復活〜	ONI Rei ~Fukkatsu~
DS	2007-08-30	ONI零 戦国乱世百花繚乱	ONI Rei Sengoku Ransei Hyakka Ryoran
PS1	canceled	ONI零〜流転〜	ONI Rei ~Ruten~
Arcade	1995	隠忍 ーザニンジャマスター	In'nin —Za Ninja Masuta–

The one game that actually released for PlayStation came out in 2001 and was called "ONI Zero ~Resurrection~"; thankfully it wasn't for the PS2, which might have been confusing since the romanized "ONI" was used on Oni's Japanese box too. A 1995 arcade fighting game loosely based in the same universe was called Oni: The Ninja Master. Despite the game's subtitle already being in katakana-ized English, it was released in the Western world with the inscrutable name Metamoqester.

Also in 1995, the game universe was the basis for an anime OVA called "Touma Kishinden Oni", consisting of 25 10-minute episodes released on five discs. Incredibly obscure and hard to find, the opening can be seen here. It's about a young warrior who has to come to terms with his inhuman nature and ability to transform into an "oni".

Halo's ONI

See Easter eggs – Halo.

Street Fighter's Akuma Oni

Oni (sometimes called Akuma Oni or Oni Akuma for clarity) is a "demon" form of long-time Street Fighter character Akuma who has been corrupted by the dark energy of his martial art. He first appeared in Super Street Fighter IV. There is also a Pandora's Box variant of Oni in Street Fighter X Tekken.

Urusei Yatsura's Oni

In this anime, "Oni" is the name of an alien race, but the name isn't mentioned much. What's more important is how the myth of the oni influenced the design of alien character Lum, so see Oni (myth) – Aliens for information.

Agent of Mayhem's Oni

Agents of Mayhem, an open-world action game set in the Saint's Row universe, has a cast of 12 playable characters including Oni, a Japanese hitman.

AT-43's ONI Corporation

AT-43 is a role-playing board game with a faction called O.N.I., standing for Okamura Non-aligned Industries. They're a mercenary corporation that creates zombie soldiers and builds weapons based off any technology they can get their hands on, then sells them to the highest bidder in the war between the other factions of the game.

Also not Oni

Oxygen Not Included

A survival game set in a space colony. No connection to the concept of the Japanese oni, but abbreviated to "ONI" often enough that it competes for attention with Oni in search engine results. We even had to change our Discord server's name to "Oni (Bungie, 2001)" to prevent confused Oxygen fans from joining.