This is one of those cases were I'm just stumped for answers, not sure who is right, could go either way.
Doesn't look like a high stakes case at face value. But if you look at the components individually, there's a lot of the most difficult elements. International law, the three powers interacting, intellectual property...
The matter of the dispute seems inconsequential, but my subjective opinion is that IP often uses a lot of the same judicial mechanisms that higher stakes civil and even criminal cases use, IP is often the guinea pig of the full extent of the law, you'd think it's the other way around, but cases like murder and CSAM often rely on good will, common sense, shared notions of right vs evil, journalism. In cases like IP disputes, whatever judgments are achieved, are done through an almost exclusively mechanistic implementation of the law (with modestly deep pockets fueling the machine, sure it's big companies, but let's not pretend nintendo, LaLiga or even Hollywood run the world).
I'm leaning towards fair use, I haven't seen the actual memes, but if it's truly a meme, that would be transformative. So it wouldn't depend on the fact that one party is an executive branch representing a country, nor the fact that there's two different legal systems. That said, fair use is an American concept, not sure Japan has that. At any rate, this is all mostly American jurisdiction, so if by American courts this is legal according to American rules, Nintendo has an American subsidiary, sells to the US. I'd lean towards there not being a case, but I can see how this might be Nintendo's standard strategy in pursuing a loss-loss scenario by wasting time and lawyer fees in an inconsequential manner. Kind of like a chicken game in game theory. As far as I know the optimal counterstrategy are counterclaims, and claiming legal fees, that would be a legal battle I'd spectate with a popukoruno baketo