The player learns more about her family and origins while battling both the TCTF and its greatest enemy, the equally monolithic criminal organization called the Syndicate.

In the game's climax, Konoko discovers a Syndicate plan to cause the Atmospheric Conversion Centers, air-treatment plants necessary to keep most of the world's population alive, to catastrophically malfunction.

Power-ups such as "hyposprays", which heal damage, and cloaking devices, which render the player invisible, can be found scattered throughout the levels or on corpses.

Since the player can carry only one weapon at a time and ammunition is scarce, hand-to-hand combat is the most effective and common means of defeating enemies.

As in Bungie's earlier Marathon titles, tiers are color-coded, in this case by green (weakest), blue, and red (strongest).

The explanation for her superhuman abilities was changed to be more organic with the addition of the Daodan Chrysalis concept by design lead Hardy LeBel.

Since Bungie's employees were moving to the new office location in Microsoft's headquarters or leaving the company, work on Oni had to be completed as quickly as possible.

[17][18] Some reviewers were unimpressed by the minimal detail of the environment graphics,[42] the lack of intelligence on the part of the AI in some situations,[43] and the plot, which was occasionally criticized as underdeveloped.

[45] The absence of LAN-based multiplayer, which had been demoed at hands-on booths at Macworld Expos during Oni's development, but removed before release due to stated concerns over latency issues, contributed to some lower scores from reviewers.

[citation needed] On the positive side, Oni received the most praise for its smooth character animation and large array of fighting moves, as well as how it blended gunplay and melee combat.

When reviewing the PlayStation 2 version, Jeff Lundgren of Next Generation commented that despite the game having a longer development time, it was worth the wait in the end.

[47] The "Anniversary Edition" was made by fans and the community, based on years of research, and enhances the retail copy of Oni.