It's clear that Pokemon still has a lot of staying power, even when some doubt Nintendo and Game Freak's ability to push Let's Go: a hybrid of the casual Pokemon Go and the core games. As far as Japan is concerned anyway, it's still a mega-hit worthy of a top spot in the sales charts.
According to Media Create data, Pokemon Let's Go Pikachu and Eevee sold through 661, 240 units in its initial three-day debut: a figure that includes bundle editions with Switch hardware. The next closest game is Fallout 76 with 73,489 units sold this past week. Yep, it's a massive dropoff from there with Super Mario Party and Call of Duty Black Ops IV to follow.
The real key piece of info here is just how much Pokemon Let's Go lit up Switch hardware sales, also bolstered by the aforementioned bundles. The Switch sold 200,850 units, followed by the PlayStation 4 at 17,789 (combined, for the PS4 and PS4 Pro). The mobility of the Switch and Pokemon as a whole make for a great combination.
How great? Well, not as monumental as a mainline game. Sure the 3DS had a much bigger install base when Pokemon Sun and Moon arrived, but that duo sold a whopping 1.9 million copies in Japan the first week. Even if you outright double Pikachu & Eevee's figures to stretch it out to a week that'll still come up short, but Nintendo has to be happy with the influx of Switch sales.