>>51159722I mean it's true that SM has a weird cliffhanger with Lillie going to Kanto to find treatment for Lusamine, but USUM is an alternate series of events where that doesn't happen.
A lot of the plot points in USUM also didn't matter much in the base games, like Necrozma, Lusamine and Guzma's relationship and the rainbow rocket stuff.
That said while you can play USUM without the context of SM, there's some weird stuff that's going to seem off, like them keeping in Lusamine's neurotoxin fueled rants even though it doesn't really match with her MO in that version. And Nebbie's big climactic evolution moment is totally subverted, which probably seems weird to someone who was waiting for it the whole game.
