Rellana, Twin Moon Knight RL1 NG+7 DLC+ No Blessings Torch only

The five hit beam combo in phase 2 only has a hitbox on the beams themselves so you can just stand inside the sword slashes to avoid them although you have to be careful as to not extend your own hitbox too far back otherwise the beams will hit you which is why I aim downwards for the first charged R2 and for the final beam I strafe around to the left before doing another charged R2 which I've found makes that punish more consistent without having to worry about the final beam hitting you for no reason since I've had the final beam hit me when I didn't strafe before trying to hit her with a charged R2.

Another interesting thing about her is she never does the quick upswing with the smaller sword twice in a row so in phase 1 if she does the combo starting with the quick upswing using her small sword ending in a double overhead slash with both swords you can charged R2 instead of a regular R2 as you normally would as she won't do the quick upswing to punish you.

The last thing I would like to point out is when she's standing in the pool of water in the centre of the arena she takes less damage from fire based attacks and also sometimes during this fight it'll rain which further weakens fire based attacks.
If heavy rain occurs during the fight it'll weaken fire based attacks even more than regular rain.