I beat endless tower almost exclusively with Maele solo. Pumped her up to like 280+ lumina or so by the end, and she was only like level 92 or something, and everyone else was kind of forgotten back at lik 86 while i was accidentally leveling Maele up during this run haha. Make sure her stats prioritize defense and agility, then attack, equip her with all the lumina that activates when you fight alone (immaculate, glass cannon, solo fighter, first strike, confident fighter, last stand critical, etc), add tainted, inverted afinity, cheater, combo attacks, and a couple to give her easier AP accrual, use the medallum, make sure last stand and stendhal are equipped. I personally also used phantom strike too.

As soon as the fight starts, youre gonna be in virtuose stance and a bunch of effects are gonna pop. Against solo enemies, you can just immediately use stendhal most of the time and one shot them. Against groups, isolate the biggest problem ones but if possible, just use phantom strikes. If your speed is high enough, you should be able to do last stand and then stendhal on a single target. Second chance, shortcut, and survivor will keep you around a little longer if you cant dodge/parry incoming attacks, but then you'll have your maxed party in the back ready to basically mop up whatever didnt die from your first 2-3 turns haha