Mark of the Electric Underground has a recent video about this that I thought was interesting. I tend to think that categories have really porous boundaries, in that every time someone tries to draw a clear, solid line, there’s almost always an exception.

Games like Vampire Survivors have been categorized as “bullet hell” which… I mean, maybe. But it’s not a shmup for reasons it’s hard for me to articulate. I actually tend to think of games with free movement and vast enemy hordes as musou games!