Well, made it through stages 7 and 8... but I'm at a complete loss as to how to beat Reisen; berserk is utterly destroying me, and she inflicts it too often to juke through it via Omnidirectional Demon Binding Circle, not to mention that Lunatic Red Eyes will oneshot any non-physical characters and then some. :ohdear:
Best team for Reisen is Sakuya with the Arondight, Byakuren for buffing up Sakuya via Weapon Bless, Alice as a tank, Reimu as the healer, and the final character is up to you. Commander is whomever you want.
Accessory wise, throw an accuracy booster on Sakuya if you don't plan to abuse Private Square and make sure she has 25 points into her 2h Sword tree to have access to Full Moon Revenge. Reimu should use an accessory that makes her immune to Berserk. If you don't have that, give her the next best thing and use her other slots for +RES accessories. Any armor you have that boosts RES is good too. If you still have Berserk resistant stuff left over, throw it on Alice.
Byakuren...20 points into her Support Skill tree to get the most out of Weapon Bless. If you can get 25 points into her Scroll skill tree without giving up too much from her other skill trees, go ahead and do that if you wish.
Reimu needs 25 points in her Barriers skill tree to give her healing spells a small AoE effect + heal permanent type status effects.
Alice should be setup to tank. She's gonna be providing Parrar coverage for everyone.
Formation...Poison Shield is an excellent one to use and is not hard at all to acquire. Just have Alice, Satori, and Byakuren in a party plus whomever else you want, boost Satori's IND with Hyper Trigger, poison something and you should hopefully inflict Deadly Poison on the target. If not, arm Satori with a Green Eyes weapon (Satori's...2nd eyeball weapon I think), Arboreal Robe (+10% poison damage), and a Poison Suzuran (another +10% poison damage). That should do it. After that, let the target die from the poison.
Afterwards, go to the magic circle right before the stage 8 bosses and bam, Poison Shield formation. Alice should be taking point while everyone else is arranged behind her.
If you don't feel like going for that, Sunshine Launch is a decent alternative, but you'll be more at risk from Reisen's attacks that hit a line.
Skills...
Alice - Marionette Parrar, Hourai Doll, Little Legion (If she's learned this. Don't worry if you don't have it)
Byakuren - Weapon Bless, Never Fail if Sakuya still has trouble hitting Reisen, Light & Dark Heals if she's a high enough level
Reimu - Ofuda of Healing, Omnidirectional Demon Binding Circle, maybe an attack spell so she has something to do when not needing to heal
Sakuya - Full Moon Revenge, Private Square
Now then, battle starts. You open with a Weapon Bless from Byakuren on Sakuya so she can hit Reisen HARD with FMR. Your looking at 1000+ damage a hit at least if Sakuya is at a good level and has that Arondight equipped.
Meanwhile, Alice should throw off Hourai Doll while Reimu can cast ODBC or poke Reisen, whichever you choose.
Next turn, heal up the injured, have Alice spam Parrar from now on.
Basically, Sakuya can end this fight herself in 2-3 turns max with the damage she dishes out.
If you still have problems, make Aya your commander, fire her 3 bomb support spell off, Private Square with Sakuya, own Reisen with FMR spam.
Hope that helps.
As for me...cleared stage 12 today. I actually took down the bosses the hard way. Was tricky and took a few tries to develop my strategy, but it worked. Sakuya ran out of MP at the end and a couple other characters came close to it though.
Stage 13 comes tomorrow. I know I'm gonna hate the Elec Breath spamming things that pop up here, I just know it :ohdear:.