Settled for A-ranking this week's trial with Kitty Clarissa/Charles/Achates/C. Domi (C. Domi just being my highest single target DPS).
This fight is completely unreasonable and asks for both an absurd amount of cleansing and an absurd amount of single target DPS to get anywhere. If you don't have someone who can keep immunity up permanently (when it isn't cleansed by Nilgal's S3) he'll just constantly steal turns and make it literally impossible to keep up with the volume of debuffs... and I honestly have no idea how you'd keep immunity up for that long considering how fast he cycles turns. Maybe if I had a 200+ speed Vivian or something (which would, amusingly enough, make her completely useless as a cleaver).
My 152 speed Angelica is, unsurprisingly, completely useless here, and so is my Angelic Montmorancy (who becomes more a liability due to the fight penalizing every turn you perform a non-attack skill). Destina is a no-go due to the long cooldown on her S3. Achates alone obviously can't keep up even partly well, hence me throwing in Kitty Clarissa hoping to eke out something of a win.
Honestly, I'm just not a fan of the Hall of Trials. Kayron was already obnoxious enough with his constant self-cleansing (seriously, why did this need to be a thing?), but now we have to somehow have super cleanse + super immunity + super speed + super damage and I am just wondering why should I even bother at this point. That's way too much work for very, very little reward. Congratulations to those of you who happen to have the few specific compositions that actually work against this nonsense.