Whether you played the original Pokémon Yellow or you've never touched a Poké Ball in your life, the two new Pokémon: Let's Go games are a great way to practice your Japanese skills and learn new words while you're at it.
When starting up the game, you have the option to choose your language. When you select にほんご, you can decide if you want to play in kana or have kanji as well. If you're a kanji pro (from using WaniKani), you'll probably find the kanji option much easier to understand.
We know you're going to play it anyway, so why not improve your Japanese at the same time?! ポケモンゲットだぜ！
If you're familiar with Pokémon, especially Yellow, then the content will be similar enough that you should be able to make your way through the game while focusing on the Japanese instead of the gameplay. And if you're one of the many people who have trouble with katakana, there's no better place to get exposure than the katakana-rich world of Pokémon! If you're having an especially hard time figuring out what a Pokémon's name or move is, there's always this Pokémon-specific dictionary, so learn learn learn!
Not only will you have to understand what a move's type is to win, but you'll be seeing the same moves over and over—built-in SRS! And the game is designed for kids, so you'll see a nice variety of text, most of which is fairly simple.
Honestly though, we know you're going to play it anyway, so why not improve your Japanese at the same time?! ポケモンゲットだぜ！