They're a bunch of artwork about this new Touhou girl ZUN announced. I discovered this because someone at my discord points it out and already sharing fanart about this "mike" girl.
While I don't play much of Touhou game, I did play the quote on quote "Priated" Demo version of Touhou 18 as the same person send a link to it. It kinda fun but bullet hell isn't my genre kind and dear god, I suck at it.