Hmm, if I could make a Ryona game. After reading some of the ideas posted before hand SkyHigh's idea is closest to mine.
I'd believe the best genera for this would be survival horror, with realistic graphics akin to Resident Evil 5 or Dead Space.
The setting lays the foundation for the rest of the game, to keep with the horror elements I'd suggest a city perhaps half damaged by an earthquake of supernatural origin that affects the town. That keeps an atmosphere of familiarity but also off set the player with that familiarity being distorted, not only by the damaged buildings but by some abnormal sights (such as flesh growing along walls) to really drive the 'creepy' nail home.
For the survival elements, I'd say make the player-character relatively weak, throwing the illusion they are strong in at the beginning (when they'd be fighting thugs, and small monsters) while as they progress through the city they come across stronger and stronger monsters that can easily make mince meat out of them.
Instead of sticking the player with some preloaded character(s), I'd add a in depth create a character system, allowing the player to choose things like: Gender, voice, body structure, facial structure, clothing, height, weight, age, the whole nine yards. I say make a system that lets the player make any character they can think of. So for those that want to create just someone sexy, or if they want to create say... Tifa Lockhart, the options would be there.
For ryona elements; all enemies have 'throws' effectively attacks that cause them to latch unto your character and damage them, at this point their movement gets locked and the camera moves to focus on how they are attacking. Say a thug starts strangling you from behind, the camera zooms in to show your character struggling to get his arm away, or if a dog bites your leg it zooms in to show it's jaws tearing your flesh up.
Also many later enemies would have instant kill attacks, or pseudo-IK's. Obviously if you get hit with an IK (like a T-Rex's mighty bite) you're dead... a 'pseudo-IK' would be a two part attack, (like being knocked down, then stepped on) or simply an attack that kills you at low health (like the hunter gammas in Resident Evil) all attacks, IK, pseudo-IK, or normal, all attacks have nice animations with they reduce the hero's health to zero.
Lastly, enemies. There'd be something for all ryona fans; beating, torture, guro, vore.
Enemies that are both normal (humans, bears, wild animals, dinosaurs) and abnormal (mutated creatures, or non-phyical beings like ghosts, or large impossible beings such as 'meat walls' with tentacles)
Inside some buildings you can fall into traps, fail to escape them and you'll be treated to a torture sequence, and possible game over.
I'll stop here because I don't want to drone on detailing every little detail I'd like in the game... if anyone wishes to comment please do so however.