Oni

Although fearsome in appearance Oni are the dual natured Japanese creatures of legend that represent both the demonic "destroyer" and the godlike "protector".

The Shinto Oni was originally more god than demon but the perception of these helpful spirits changed to become gradually more mischievous. They became associated with misfortune (analogous to storm gods) and later became incorporated into the new Buddhist concept of Hell. Oni became the guardians of Hell, torturing and collecting the souls of the wicked, swooping down from the sky to take them from those who are about to die.
Aspects of the protector side are still apparent with many traditional Japanese houses having a tile shaped like an Oni's face (known as Oni-gawara) placed on the roof to protect the home from evil.
Many festivals are led by marchers wearing Oni masks who walk before the processions, driving away any evil spirits.

Oni (for PS2)- Video Game Review

As good as Syphon Filter 2, but...
...it lacks the accuracy in shooting as well as the random directional shooting while you are running. The hand-to-hand combat in ONI requires some time to be accustomed to. The movements are somewhat awkward at first. One thing this game lacks majorly is a good story. The setting is unclear, the "raison d'etre" seems non-existent...other than "violence for the sake of violence", what other reason is there for the main character to be so passionate about her missions??? There needs to be storyline development in the beginning, just like how Final Fantasy 8 and 9 were. The graphics are okay, but being PS2, it should have been as good as those in DOA2 Hardcore. Despite the lack of these value-added features, the game overall is indeed quite interesting. The execution of this new 3-D concept of involving hand-to-hand combat and shooting was very well done and I feel it was long overdue. I'm certain the sequel will have the features I've mentioned above to improve the overall gaming quality.

Oni (for PC) -- Video Game Review

As I am with all single-player-only games, I was a little disappointed with Oni. I mean, after Quake, one expects the game to go on in some respect (for fps's, usually online deathmatches) forever. Oni, unfortunately, is single player, period. It also suffers from many of the design limitations placed on it by being a PS2 game -- save points, set controls, very little graphics customization.

That said, Oni is an absolutely fabulous game. It manages to overcome these shortcomings, which with a lesser game would have made me take the thing back.

The story is, like many video game stories, just okay. About on par with Half-Life's story: just solid enough to keep the action going. Nothing extraordinary.

The graphics are absolutely stunning. I can see how it would be a little disappointing on a TV with the PS2, but on a gaming rig with the graphics turned way up it's fabulous. The levels are massive and render perfectly, the fighting effects are both cool to look at and convey very detailed information, and the character models are very lifelike. It's obvious the designers put a lot of thought into how the player figures out what's going on. There's two little hud graphics that convey all your vital statistics without resorting to a huge bar across one side of the screen. The compass feature in the left hand hud prevents you from getting too lost in the levels you're exploring. And while fighting, the flashes of light that appear when your shots land tell you how much damage you've caused your opponent -- without putting a lifebar over everyone's head.

The fighting is a lot of fun. You only have a few options with respect to weapons -- either you use the one weapon you can carry at a time, or you go in with your fists. This creates the situation where most of the time you are playing the game like a fighting game. You don't get a lot of ammo in this game, so don't expect to run around shooting everyone. You've got to spend some time practicing combo moves to get through your opponents.

So, overall, well worth the US$35 you'll end up spending on it. Definite minuses because of the lack of control customization (WASD or nothing) and it being single player only (I'd love to go online and duke it out with some others or try some of those levels working as a team). But these are outweighed by the quality of the game play.

flamingweasel mentioned that the controls are unconfigurable, but this isn't quite correct. While there is no config in the game itself, you can change the keys with a little effort.

Buried in the data files is a config file, similar to Quake's config files, where you'll find a list of key bindings. It goes something like this:

...
bind w moveforward
bind s movebackward
bind a turnleft
bind d turnright
...

The things the keys are bound to are just an example, and probably not what actually appears in the config file, but they should be similar. To change the keys, just change the token that appears after 'bind'.

The Shinto and Buddist Oni were divided into two types:

1.From Hell, called :"Gaki".
2.From Earth (Oni)

GAKI are able to take a somewhat humanoid shape, but usually are not able to hide their huge swollen bellies. They are red or green and have the head of either a horse or an ox with three eyes and grotesque horns and talons.

They are constantly tortured with raging hunger and thirst.

They pounce upon the wicked who are close to die and send them to the torment of Hell.

ONI are earth demons who can shapeshift into a human form of a relative or aquaintance, of the person that they want to torment.

Some of these are rumoured to be the distorted souls of women who have died of excessive grief.
These demons are responsible for bringing misfortune,and disease - especially the plague.

They may be driven out during the "Shinto Oni-yarahi" ceremony.