アナスタツス (Anastasis) has 65,000 HP. She is weak to Sword and Lightning attacks, and resists Fire and Ice attacks. She has an innate regeneration of 999 HP. She has 300 Physical Defense and 50 Magic Defense, so a Magic Attack approach is recommended.
Recommended party: Sakuya, Sanae, Marisa, Patchouli, Alice, Nitori as commander.
Before walking into the fight, make sure you have as many Lightning attacks as possible on your Marisa and Patchouli, but make sure you only have one spellcard of each. All spellcards are on the same cooldown timer, so it's advised to choose your strongest Lightning spellcard and the rest of your attacks be nonspellcards.
Marisa should be going in with 恋の台風 (Love Typhoon(?), level 42), Stardust Surge (星屑怒涛), and Stardust Missile (スターダストミサイル). She should also be equipped with as many +Lightning damage items as possible: The Bardiche (バルディッシュ, obtained from the magician fairy enemies in Stage 7) raises lightning damage by 20% and the Raiden Amulet(?) (雷電のアミュレット, obtained from the demon girl enemies in Stage 7) raises lightning damage by 10%, for example. Marisa should have 25 points in her Astronomy and Magic Mushrooms trees. She should also have a +# bomb accessory - which one is up to your personal preference and what you think you need.
Patchouli should walk in with Thunderstorm (サンダーストーム, level 36), Thunderbolt (サンダーボルト, level 27), and Call Lightning (召雷, level 46) as her attacks of choice. She should also walk in with Active Elemental (アクティブエレメンタル, level 9) and Heaven's Crack (ヘブンクラック, level 13). She should also have 25 points in her Spirit Magic and Magic Mastery trees.
Sakuya should have Full Moon Revenge (25 points in Greatsword/Two-Handed Sword) and Private Square (プライベートスクウェア, level 10) with 25 points in the Time Stop and Greatsword/Two-Handed Sword trees.
Sanae should have Prayer's Wind (祈りの風, level 8), Shield's Wind (盾の風, level 10), Miracle Fortune (奇跡のおみくじ, level 24), Super Healing Miracle (超回復の奇跡, level 40), and Star Ritual to Call the Godly Winds (神風を喚ぶ星の儀式, level 36).
Alice should have Marionette Pariel (マリオネットパラル), Little Legion (リトルレギオン, level 28), and a nice resistance to Blunt-type attacks. Optional addition is Hourai Doll (蓬莱人形).
Nitori's gear typically doesn't matter, but make sure she has a decent bomb pool, preferably in a multiple of three (3, 6, 9, etc.).
Recommended formation is the Phoenix formation (鳳凰天舞の陣), with Alice in the center. Marisa and Patchouli should be in the back rows to exploit the Magic Attack+ bonus.
The first few turns should be spent maximizing the Lightning manipulation on the Land bars. To do this, you can use Patchouli's Heaven's Crackl to manipulate Lightning on the first turn, and then follow up next turn with Active Elemental to maximize the land in two turns. Once the land is properly manipulated, Patchouli should be firing off Thunderstorms and Thunderbolts. Marisa should be using Love Typhoon whenever possible, and Stardust Surge when it's not. If you're being friends with the RNG, you'll get a few doublecasts during the course of all this. Sakuya should be using regular attacks, as her role for now is just to curb the HP recovery that Anastasis has. If you're lucky and get a Last Word on Marisa, then by all means use it and then have fun with Full Moon Revenges.
Alice should be using Marionette Pariel on the front line for the most part, as it is unlikely that the backline will get attacked. Sanae should immediately start with buffing everyone's Defense, and then follow up with Magic Attack and Maximum HP buffs. Her role throughout the fight is to maintain buffs and maintain HP as needed.
Once you get Anastasis to around 1/4th HP, Anastasis will start using a Last Spell each turn. This move is a single target move and it WILL kill anyone it hits, so this is the part where you begin using Little Legion and Private Square to minimize casualties while Marisa and Patchouli take care of the remaining HP as quick as possible. If things get really messy, you can use Nitori's 3 commander bomb to neutralise the Last Spell as well. If all goes relatively well, then the only casualty you'll have will be Alice, but that's to be expected.