Yup, The Pokemon Company has released an official Pokedex app across iPhone and iPad on the Japanese App Store. It's not a "new" app, mind; people are saying that this is a port Pokedex 3D Pro, which landed on Nintendo 3DS this July in the Japan. The iOS version is a paid app with in-game purchases.
If you're new to this whole Pokemon thing, a Pokedex is basically an encyclopedia that has all sorts of information about the little monsters that populate the series. This one in particular dishes out info on every Pokemon that has been in any game in the long-running series. It also has nifty animated 3D models of each, if you're into that sort of thing. The catch is that certain "sets" of Pokemon are locked behind IAP. Kotaku Australia reckons the app will run people $20 if they want everything.
The Pokemon Company is a subsidiary of Nintendo, so this isn't exactly a Nintendo app. It's probably of note that this is the second app The Pokemon Company has released on iOS.