Yeah, having weapons from the Touhou games would help a lot. Even just reskins would go a long way. As for enemies, there can probably be more variation in enemies types than the main series, since everyone just resurrects in this world. You could probably use species like tengu and kappa and regular ol' human.
I think it'd help to integrate more Touhou characters into this world even if they're not plot-relevant or assassination targets. For example, in this universe Alice could be a robotic-soldier manufacturer who sells her creations to various companies & branches, and some levels could have her dolls as generic enemies. Maybe they'd have less health than other enemies (like so weak that even your starter gohei oneshots them?) but be way more sensitive to noise. I think something like that, applied to a handful of characters, would really elevate the worldbuilding.