*asking for advice*
I don't know if I'm good enough to give advice but perhaps you can make some use of it.
When one of those waterfall parts come, stand on one side of the screen and slowly stream to the other, if you're about to hit either side or one of those light blue bullet waves, do a quick move into the direction you were streaming to and then stream to the other side. I'm not sure how exactly to explain it, you just gotta practice it. Though I can tell you that it doesn't always work for me either so if it comes down to it, bomb it away.
Momiji might be quite menacing on first glance but once you played her a few times, it's not that hard. Don't quote me on that but I think the patterns are static (at least the huge ball rings should be) so make sure that you're in the middle/more to the right when she appears as the first huge ring will fly to the bottom left; stream the fairies before accordingly. Otherwise it's basically just left-right-left-right while avoiding the small bullets. Don't squeeze yourself to the bottom of the screen, try to stay a bit more above so that you can retreat if you notice one of the gaps closing in. Dodge, go back up, look for the next gap, rinse and repeat. Bit of practice and she becomes easy.
The three fairies spawning the small star pellets I can't really help you with, that's pure dodging. Try to stay beneath one until you got rid of her and slowly move to the next one. Alternatively just shoot down the first one and stay in the middle.
Aya's spells on the other hand are a bit more difficult. Her first one seems to be way easier on Hard than Normal as you don't get walled that easily. Standing near her is a good idea, give yourself enough space to slowly move to the bottom if the path ahead is blocked so that you got enough time to look for another gap to fit through. Don't let yourself get walled to the bottom.
Her second one I have problems myself, heh. But you seem to have the hang of it so it's okay.
For the third one I'd advise you to hog the left bottom quarter of the screen. Kinda a bit more towards the middle of the screen so that you can - as always - retreat should there be too much raining down at once. Pure dodging too, keep at it!
For the last one, wait until the wall bullets close in on you, slip through them on either side, go through the horizontal pellet line and repeat the same over and over. Generally you don't want to dodge both waves at the same time so if possible, try to get through the pellets first and then the walls. You might want to move towards Aya to dodge through the pellets once the pattern gets a bit denser. Dodge the arrows, pellets, arrows, pellets and so on. Easy-peasy once you got it down. Going through the walls unfocused is what I do all the time but it's not needed as you're quick enough focused to slip through them too. Whatever floats your boat.
Also, as a survival player I'd advise against bombing through every spell. There's no fun in playing if you cheese yourself through the actual challenges. Learn the patterns, dodge and if you think you don't stand a chance, then you can still bomb. But don't be a lamer and cheat through everything. =P
Hope you could make some use of my methods. I'm not a pro myself but any help can do I suppose.
