i've played some touhou but mushihimesama seems like such a huge step up in difficulty,, is it?
also, have you ever 1cc'd a bullet hell?
Not at all! Mushihime-sama has tons and tons of difficulty options/modes to accommodate new players. It's actually the #1 game I recommend as someone's first shoot-em-up for this reason. Its novice modes perfectly teach and acclimate new players in a way that is accessible but still engaging (the second half of which many beginner shoot-em-ups tend to fail at). The harder difficulties of course get as hard as the lunatic-mode Touhous, for example, but the gradient curve to get there is a lot more smooth and enjoyable than basically any other shoot-em-up I've ever played (or am even aware of). So to answer this question: yes and no! It manages to be perfectly tailored to every player and what they're comfortable with/ready for, from new players to masters. Friends of mine who have never touched a shoot-em-up can attest.
As far as 1CC's, Mushihime-sama was actually my first one ever, lol. Being able to conquer the novice modes gave me the courage to push through and 1CC some of the other difficulties too, but I don't think I managed to climb up to the absolute hardest modes. Other 1CCs... I've 1CC'd some of the Pocky & Rocky/Kiki Kaikai games of course, but those are like a danmaku/run-and-gun fusion. Most of the time I play shoot-em-ups to the extent that I understand their systems and functionally know what I would have to do to 1CC them, but never quite put the time in to do so. I've probably 1CC'd R-Type Final I played it so much, but I don't remember going in with the deliberate intention to do so. That may have been incidental. Plus some easier ones like Magical Chase and recent indies like Hazelnut Hex which are made to be accessible. Ones that can be 1CC'd without thinking about it. Currently though, I'm trying to 1CC Lotus Land Story, the fourth Touhou game. That and the sixth game (which is on my top 25) are my two favorite Touhou games, which I do feel compelled to put time and effort into compared to other shoot-em-ups. I'm noticing the trend between the games I go out of my way to 1CC is that they're all cute...