Earlier quoted context omitted.
There are quite a few open source or royalty free Japanese fonts (Google Fonts has 50[1]). But, as everyone else has mentioned, font usage in games (and most creative visual works) is more particular than just the bare minimum of "does it actually render the glyphs". Imagine if all text in your favourite game was all Times New Roman, it would make the game worse. [1]: https://fonts.google.com/?lang=ja_Jpan
Alternately, imagine if all text in your favorite game was IP owned by some random third party that could ruin everything one or two years down the line. Perhaps it is time for more people to invest in royalty free IP? We are seeing a bit of a tragedy of the commons type of situation going down, right now.
I guess the trouble is that game companies can't really band together and pool money to make a good font since the point is to look unique, so this only works for the largest studios. Otoh, at least for now, the smaller ones might stay below the 25k user limit