Advice for Door of Void: The Arrival of Seven Sins

I would try with this
Medea, Mash, Merlin (supp)
Kuro, Ozy & Kintoki rider
I'm not the best to ask but i think this could work. Also you can go with combat suit to switch ozy in after the third room.

Ozy + Hans + Merlin or Mash should work if you manage to protect Ozy in the first wave.

My team was Kuro (Kaleid Saphire) + Kouhai ( Prisma Cosmo, but not necessary) + Suport Merlin ( Prisma Cosmo, Helps a lot but wasn't necessary).
Mystic Codes: Atlas Academy Uniform, Saved me once time when the enemys focus in killing my Mash, but I didn't let this continue.

The strategy is ARTS CHAINS, preferably full NP of all, Kuro does damage and the others keep her alive. Taked to me 88 turns, was easy to me, minus two issues:
1: The Homunculus of the fifth part, Caligula dead fast, but kill the others leave much time and have to use the focus target of Mash to preserve Kuro.
2: Amakusa TPK, was my falt, but not killing him very fast can destroy the strategy, my back team was good with Jalter to Kill him immediately, how you haven't her, I suggest that use Chaldea Combat Uniform instead Atlas. Save Merlin or Mash with a scapegoat of the reserve team, I preffer save Merlin because the cure of NP.

You don't need to use any command spells or use SQs to finish the Challenge Quest and your servants are decently leveled, even Ozy and Mashu and Hans is maxed.

If you want specific team set up, go with Ozy + Hans + friends Merlin ( 2030/Prisma Cosmos ) + Elizabeth Saber + Mashu + Nero.

- Ozy with Buster/Crit UP/Atk Up/NP UP CEs is more than enough, Joint Recital or Golden Sumo or Holy Night Supper or Victor of the Moon or Partake with the King is one of the best CEs for Ozy. For me, i'd go with Victor of the Moon and HNS.
- Hans with Crit star gen CEs or Def Up or NP gain CEs is good. For example : 2030, Divine Banquet, Halloween Devil, Chaldea Lifesaver and steel training.
- Friends Merlin, for agressive and and swift kill find the one equipped with 2030. If they don't have it then go with the Prisma Cosmos one, it's for faster NP regen and safety gameplay.
- Elizabeth Saber, go with Golden Sumo or any CEs that can increase her NP damage. Back Up DPS is important here because if something wrong happen to your Ozy then Elizabeth can take his job.
- Mashu, 2030 if you have it but if you don't, use NP gain CEs.
- OG Nero, Nero have 3 times Guts with strong self healing skills and also self Atk + Defense buff. Maid In Halloween, Golden Sumo, Art Up, NP Up or Holy Shroud of Magdalene or Steel Training.
With Holy Shroud of Magdalene, you can tank every attacks from Dantes and his Invincibility pierce is not enough to kill Nero.

I've done some CQ runs with :
Squirtoria + Hans + Mashu, D'eon + Chloe + OG Nero.
Martha + Hans + Mashu, Ibaraki + D'eon + Heracles.
Gilgamesh + Hans + Merlin, Chloe + Mashu + Heracles.
Kintoki Rider + Hans + Merlin, Ibaraki + assassin Scathach + OG Chu.
Scat ass + Hans + Merlin, Kintoki + Helena + Heracles.

Until now, i have clear it by using different DPS. The easiest was Gilgamesh + Hans + Merlin.

Putting any DPS + Hans/Mashu/Merlin is a no-brainer team. Don't forget to add a backup DPS on the backline.
The battle is pretty long and using Hans and Mashu and Merlin is a way to guaranteed your Victory. For safety, use Atlas Academy and Combat suit.
Your master/pilot skills is also one of the biggest factor, you're the mastermind and those servants can't act without your orders.

Kiyohime+Mash+Merlin. Ozy and Kuro as backup damage dealer. Merlin will help with NP charging and healing, Mash will protect Kiyo from harmful damage while Kiyo can burn all of those liar to hell 😁😁😁

either use kuro+memelin supp, or borrow some dps dealer with your hans/medea lily+kouhai