You're on a difficult position right there. You can change your setup but it could turn out to be less efficient, also you have some chances of getting spooked by Fionn or even Vritra at some point.

If you don't want to get screwed by Instant Death, then maybe these can help.

With Plugsuit, you can use more support and doing this with 50% NP charge, but I guess this is quite enough.

If you want to use a lancer and don't want to use Arash or chen I'd say you're out of luck unless you have Parvati and skadi.

If OP is okay with 3 free slot or less, then Romulus and Hektor is a good choice too.

Would say Activate S1 art up for first two wave, only enable S3 only on 3rd wave since Servant only exists on there anyway (exclude those shadow servs)

And a NP starter CE like Dragon Vein / Imaginary Element since Kaleidoscope is not everyone can have. Plugsuit if necessary.

P/S that sidebewb Ascension is so good even for welfare mmhmm

I see you have a grailed jason, he loops better than erice without caring about the insta kill, but i think you are using lancer is because is in Shinjuku 2-chome, on this node you can gong them to 3 turn the node, with double castoria, waver, nero and another arts buff like mozart or tamamo, you will also need one castoria NP for the last node or gong NP overcharged by 1

This is the one i uses for that node.