parade of hassans

there is a couple of ways, if you have a medea, she will help you a lot. She can remove the death/kill buffs with her rule breaker. You also will want to bring iri to keep her healthy and alive as well as keeping your art spam going. If you have access to da vinci, da vinci is a hard counter to the hassans, debuffs and death mean nothing in the face of a genius. That said, bringing along a tamamo will help out immensely regardless of those two methods. There might be other quirky ways to deal with it, but those two methods are the most reliable.

You...don't have casters? You...don't have something to cleanse them? You...don't have buff removal?
Anyway seriously...
This is impossible with such a team. This isn't actually hard, it's just attrition honestly. You need three thing to create this attrition. Healing, buff removal and debuff removal and you current team doesn't have any of that. Yes Archuria has healing, but Hassans like stacking debuff, and even if they don't have much damage those tons of defense down would insta kill anyone if they NP.
I suggest running your waver, a support Medea Lily and finally a newly raised Medea caster for buff removal of the main Hassan since they would kill you.
Running an offensive caster, Medea Lily, and another defensive support would be good, but yeah. This team would just be destroyed. You don't need the white rose CE for this, but rather those that I mentioned above.

I used nero iri and tamamo. Keep everyone alive. Iri uses np, nero kills everyone including boss with np (important), revives with little hp. Enemy respawns. I heal nero and stabilize while fighting normal mobs. Boss appears, iri np, nero np, rinse and repeat. I think you can do this with any aoe damage np caster instead of nero.

It's just like what people have said. This isn't a damage fight. It's a survival fight. You want defense buffs and healers and someone to knock off those instant death buffs the main hassans have. Medea is very helpful for this fight but I did it with Irisviel. Instant death failed each time for the enemy because I always have guts.

Hans will work if you don't have access to Iriviel or Medea Lily, but you want healers for this fight or you're just going to run out of steam. Also one of the few situations where you may just want to go mono caster to outlast the enemy.

I was an idiot and didn’t understand the mechanics of the quest at first but still got through it on one try. How? Medea Lily + Waver. They are so so important to clearing this quest!

Waver can buff the whole team with his attack up skill but also, more importantly for this fight, his defense up skill. His NP is extremely useful for delaying the Hassan NPs and inflicting defense down and also for possibly stunning them. Make sure to put him in your starting team with a guts CE and avoid using him to be the last hit on anyone until the very end.

Medea Lily truly shines here. As an NP spammer, she heals like a boss on almost every other turn or so when equipped with a NP gain up CE. She also has a skill that heals your team for 2,000 hp AND takes away the debuffs. Her Ephemeral Love skill is great for adding extra healing to the servant that needs it most, but be catious of the long cooldown. Don’t let her get the last hit on a boss Hassan!! She is the most important component of this team hands down. If you don’t have her, use her as your support servant.

As for the rest of the team, use caster damage dealers if possible, and if not, then berserkers or something else with high damage output. Place guts CEs on them (like the Princess of the White Rose) so they will survive the instadeath mechanic when they deal the last hit on a Hassan, then heal them up to nearly full health with Medea Lily.

My team was:
-Medea lvl 60 + Magical Girl of Sapphire
-Waver lvl 90 + Chaldea Lifesavers
-Nursery Rhyme lvl 80 + Halloween Princess (who died immediately on first boss Hassan because I didn’t understand the mechanics like an idiot)
-Nitocris lvl 60 + some arts CE I don’t remember (who also died to a Hassan)
-Ilya support lvl 90 (who also died to a Hassan)
-Vlad III lvl 90 + arts CE (who died before the end due to being squishy despite his guts)

With that team, I barely made it, and I mean BARELY (Waver was the last man standing and killed the last Hassan with 250 health remaining before the guts triggered), so if you prepare better and equip CEs that have guts, you’ll do perfectly fine.

To be honest i dont know if you can with that team, i have a medea grail lv90 10/10/10 that can help you

If you're still having trouble with this, try this out because it worked for me.
Caster Marie with Hans and Waver support with Halloween Liz in the backline. The key here is to have either Marie or Liz kill off the Hassans with their AoE NP and staying alive with Marie's Invulnerability or Liz's extra guts skill and keeping them relatively healthy using Hans' NP heal and Waver's def buff.