Unless you want to make things hard for yourself, the second form basically requires Alice+Youmu+Byakuren. Give Youmu one headshot goggle and the Kusanagi (or her god slaying katana, but kusanagi is just as good if you don't need it in phase 1) or you'll cry at the very end, and I highly recommend Byakuren's All Up party buff among the more obvious Dark Weapon and patk and heals (Actually, use her RES buff on youmu too if you've got any more slots, but it's not super important- it stops Vortex though). The rest of that party's survival support is flexible based on what you want in your first party. And when you're going into the fight- don't forget to put both parties in the correct party order for your formation! If you're using poison shield that's pretty easy though since you just put the tank first iirc.
The summon roulette can bring up annoying minibosses. So, just DON'T KILL THE MORE HARMLESS SUMMONS. If they're crocodiles or snakes, leave 'em the heck alone. If it's a turtle, well, that's gotta go, not much choice there. You shouldn't have to worry about minibosses most of the time since you'll only have to deal with a few summon roulettes this way. A couple of them can be killed really fast at least if they DO show up, but it's taking time away from the actual fight.
Anyway. First form, Anastasis does some pretty scary stuff, so you need some method of handling her spellcards, whether it's Duplex Barrier, Aya party evasion blinktank, timestopping past it, Satori's Shield Wall, Nitori commander bomb, etc. Her mdef is very low and she has the least Divine Barrier so she is the easiest sister to damage, magically at least; Mad Thunder deals hella damage, although I don't recall if it bounces it's damage onto the summons... Nitori chasing works very well in part 1 of the fight overall if you don't care to have her commander bombs for phase 2.
Biotopos has more mdef and Divine Barrier, less pdef. Fujiyama Volcano works well for her FISTING WEAKNESS if you don't want Mokou (commander or inparty reraising) for revives in the second party. She's got Mad Thunder, so you want your main tank (Dodgetank Aya works, since Alice is needed in party 2, but you can build any durable character for it) wants some elec resist, other than that she's pretty boring iirc.
Lithos has higher mdef and iirc a staggering 40 Divine Barrier (see a pattern?) so even physical attacks against her low pdef and hitting weakness don't do super high damage unless you have exorcism; tanky as f. She still has status effects and Vortex and such so you don't get to decide you want Sanae in party two, you need that RES buff and status healing skills, and probably resist accessories on her so Sanae doesn't go out of commission unable to fix up your party. If you've got Reimu in this party, you might want her status barrier.
Second time around, Anastasis and Lithos seem more likely to charge up their specials, and Anastasis will kill you if you don't have the defensive measures I mentioned earlier. Other than that, everything goes about the same.
PHASE TWO. Kill it in 9 turns or you're gonna die harder than ever before, no questions asked. No weaknesses anymore, but they have a 666 damage petrification attack, so your tank needs some MYS resist to reduce that to a survivable amount and petrify resist. They've got like... that, Earth Shower (which is also painful all-target earth damage), and stuff I don't remember mattering at all. It's mostly just a damage rush. You -need- to be able to kill this in time so save those bombs! Sakuya's Timestop can mess up their pattern and buy you a little extra time, but it also winds down all of your party's buffs, so it's not necessarily amazing. A good chaser party can blow this phase out if Satori's in it using Mad Thunder, otherwise stuff like Fujiyama Volcano and Sakuya should be able to seal the deal. If you get them next to dying ahead of time, swap to Party 2 and start buffing Youmu up. If patchy is in party #1, after you get some damage out use Void Spirit to CLEAR THE LAND. CLEAR IT, CLEAR IT NOW. KEEP IT CLEAR.
PHASE THREE. Your tank still needs petrification resist. I think she has one spellcard that can sorta do instant death too but I don't recall it ever landing? Manipulating for dark is fine (the boss regens in light), but you need the 4 other elements to stay neutral or you die. Youmu is all the damage you need, just have everyone else present do their support thing. Patchy or Satori can cast opposing element magic (or Patchy's Void Land) to keep the land in check, but you should be able to damage rush her if you just went in with neutral land, so Patch isn't required (although it does add a little risk). If the land gets too high, use panic survival skills like Mokou/Nitori 3 bomb commander skills or Little Legion, Starlight Barrier, etc, but... the boss's land counter isn't guaranteed to go off the first turn it can, so it's a gamble whether you pick the right turn and live or do it early and die due to inability to stop it. Fixed 777 damage to all and big heal to herself from eating the land power. RIP.
You want either Reimu or Satori in this party for support like LOTS OF HEAL SPAM and emergency damage prevention to stop people from dying while Byakuren uses a heal instead (if you teach Satori Area Heal and Reflect Wall or Starlight Barrer or Leaf Shield; if she doesn't have any of those, she may as well stay in party 1 with mad thunder) and a commander with actual helpful bomb skills like Nitori, Mokou, or Aya. You can't revive people at all if you don't bring Mokou, Nitori adds serious survivability for if you get into a pinch, and Aya lets your healing go first so you don't die. BTW, if you have a spare turn for it while someone else prevents damage, I like using Alice's shield boosting field here, as it's basically a global party durability boost. ARE YOU USING THE AEGIS SHIELD? YOU PROBABLY WANT TO MAKE THE AEGIS SHIELD. IT'S WORTH THE COST
First party's commander is just whatever schmuck didn't make it into the other 11 slots. Their commander doesn't really matter. Mine was Sakuya because she's useless in party 2 and didn't fit into my particular party 1 setup, and Sakuya's commander powers are completely irrelevant, so.
