Replace game freak with any Japanese game developer. You'll get the idea.
Basic prerequisites of general game development (like C++ expertise, graphics design, software engineering, algorithms, mathematics etc) apply. to put things into perspective, the amount of prerequisites is usually the stuff you'll need to get a degree in game development, and yes game developers, like most other software developers are degree holders at the very least which implies at least 3-4 years of education not including industry experience. Then there's Game Freak being Japanese so there's that whole "Japanese literacy" factor.