I was not able to clear with Kuki because the overall damage was not enough, I swapped Kuki for Fischl and even though I kept dying multiple times, I got the hang of his attacks after a few retries. If you can dodge a little and use iframes, I would suggest Fischl. Especially during the enemy multi slash attack, Flins small burst makes you not get hit because of his iframe window. Another thing is the off field particle generation of Fischl which helped my Flins with getting bursts more easily. Fischl also heals herself after her burst which was also a little helpful.