I had a few issues with Iku myself...Though largely due in part to playing differently than you, and wanting to get Mad Thunder without beating her before that happened. :V
You would not believe how many times I had to reset simply because she used Thunderclap and Satori learned that instead. :ohdear:
I also didn't have Dark Sword at the time, so I had to make do with Weapon Bless(Earth). still hit comparable numbers though!
Now I'm curious though, what's the POW spread you've got everyone on? Take your time on noting it down though, I'm in no hurry. I just want to compare our runs is all.
Believe it or not, you actually motivated me into getting back into it. (Though now my time is spent on MHG, 7th Dragon III, and other such matters.)
I guess I'm lucky then. I only have to repeat twice, one because she used Thunderclap, and two because she didn't hit Satori with the Mad Thunder.
POW spread:
Reimu: I max her Barrier tree so that she can heal 3 persons at once while curing Permanent with her healing. She got decent growth in her Spirit and Concentration since I want her to strengthened her light spells, and bonus HP and RES, though she only got 3 points each in her Exorcism and Gohei.\
Marisa: I lean her POW heavily to Astronomy and Laser to strengthened her overall magic and give her slayer to Warrior, Magician, and Giant. She also got decent 7 points in her Magic and Broom, this is at the cost of Power tree because I don't use Master Spark that much.
Sanae: Balanced POW growth overall that leans towards Wind Priestess, Miracle, and her weapon.
Aya: Balanced POW growth that leans heavily towards her weapon.
Sakuya: Heavily leans toward Time Stop and 2 Handed Sword with the rest only having 3-5 POW. +135 PATK? Yes please.
Patchouli: Since she's pure black mage. I got no need to put point towards her weapon and Knowledge Storage since it increase PATK.
Nitori: Heavily leans towards Research (Chasers) and her Gun. I don't think it's worth increasing anything else since it increases so little.
Mokou: I don't know which one of her skill tree is the best. I think it's her Fist and Phoenix.
Byakuren: She's amazing at buffs, so...
Alice: I maxed her Manupulation skill tree and I have 10 points each in her Craft and Dummy skill tree. She has no need to attack right?
Satori: I don't know which part of her skill tree is better. Is it the ability to inflict Permanent which I never use, or is it the ability to inflict Variety which I never use as well? I'll go for Third Eye instead, it got PATK, MATK +30 if you allocate 13 POW in it.
Youmu: My favorite stance for her is Manussya. I so leans her skill tree heavily toward it while giving the rest of it decent POW.
So that's my POW allocation for everyone I guess.