Okay, Okuu...
There may appear to be no strategy but there are some things you can take advantage of. Knowing that the suns are aimed on the first spell, you'll want to start out under her doing as much damage as you can, then quickly shift over a bit right before she fires the first sun. (The timing I use here is on Lunatic, but I assume it can be done on Normal.) If I recall correctly, you can use the fading "Caution!" warning to help get the timing. So you move over, misdirecting the first aimed sun, then go right back under her. Now she'll fire another sun at you of course. Stay under her for as long as you can, then move over just a bit to stall for time. As the edge of the sun she just aimed at you falls under the screen, use a bomb and stand directly under her again. Now what should happen is the bomb lasts just long enough to cancel out the next aimed sun and you can sit there shooting her for a good amount of time. Wait until the next sun is about to hit you and reapeat what you just did. If you bomb too early the second time you may need to misdirect the next wave after your bomb. (I realize on Lunatic she firs two suns so the timing's going to be different and you may need to learn different timings, but I assume it can only be easier with less suns to cancel.) Doing it like that should always take only two bombs and takes almost no dodging, just timing misdirections. This is the only video I have of myself doing it, and sorry I don't know how to link to a specific part in the video. There is a link to the beginning of stage 6 in the description though, and I think the spell starts at 16:00.
http://www.youtube.com/watch?v=m6TNEy_IV4YNow for her second and fourth non-spells, there is indeed a good way to stream the bubbles as MMX mentioned. For the second one, stream the first wave of bubbles to the right and you will be on the safer side of the screen for when Okuu starts flying around. The next wave should be streamed to the left, and so on. For the fourth nonspell you use the same idea but the first wave is streamed left. If all that's too risky for you, you may try "abusing" those two nonspells like I did in that video. It's very difficult to describe so hopefully you get the idea from just seeing it.
The third nonspell should have a "safe" elevation, much like the spell after it, but it will not be the same as it is on Lunatic.
Nitori...
If you want to use only one bomb for the midboss spell, I have a trick for doing that every time. As you are streaming the fairies before she appears, quickly go to the side and rush up to the PoC just as Nitori arrives. Then quickly dash
directly in front of her and sit there for a bit. The "bullet" bullets should loop around you completely, and the circular ones will wave around on top of Nitori before they shoot out. As soon as they do (if you wanna look pro you may time a death-bomb) bomb and start backing up. That bomb will be right on top of her to deal maximum damage, and you should deplete her health before you have to dodge anything else.
For the first boss spell, I try to look for the "valleys" being formed in the streams (the low points of a sine wave graph, if you will) and stand right in that spot, though a bit up to the left. When Nitori fires her aimed bullets, just stream a bit over to the right while staying in the safespot.
It looks like Funen just jumped in before me. I don't wanna delete what I wrote, but yeah, that's the idea there.