I got the Japanese version of the game yesterday.
-Story: Etna sends a Prinny on a quest to get sweets. In the intro, you see Prinnies being tossed out of Laharl's castle (guess who)? The advertisment for this game is that "it's so hard you get 1000 lives <3".
-Gameplay: Square attacks (weak but SUPER fast). Aerial attacks are Prinny Barrage. X jumps. Jump controls are like Ghouls and Ghosts, only without the major suckage (thanks to a butt pound move, you can stop your jump at any time). Holding O causes the Prinny to spin around. If you release after he starts to glow, he runs really fast. Hold too long or release too early will cause him to get dizzy in an embarassing way. You can even charge while moving, but this move seems like a spin dash without the attack property. Triangle picks up objects and pressing it again tosses them. You can also ride vehicles. Let's just say the Netherworld comes up with some weird vehicles, such as a tank with hands with a turret mounted plasma cannon, a springy thing with a big machine gun, and a jelly fish like thing with a 360 rotating laser gun.
-Bosses: So far I've run into 5 bosses. A unique Gremlin, some big fat green thing, Mage Knight sisters (you fight both of them), a pair of death dragons (male and female each with different tactics), and a Nekomata.