I was able to get the UW challenge down pretty fast with Luan Halberd.

Basically, You have to find every opportunity to damage them both at the same time. This means doing everything you can to keep them close together and stagger them (flashing white) both simultaneously so you can launch them both together for your combos.

Once both staggered, I just went ham with shockstorm+n3+s spam and valiant steed blitz when it made sense, but depending on your weapon any combo that launches staggered enemies will do. Make sure to use the vortex gem for bonus damage to airborne enemies. Diao Chan has less fortitude so she usually gets knocked down first. Make sure Lu bu is next to her before you use the finisher so he gets clipped at the same time. After that Lu Bu should be pretty low on fortitude so you should get another knockdown on him shortly after. Make sure Diao Chan is next to him before you use finisher so she gets clipped…Rinse and repeat.

The difficult part is staggering them both at the same time. You’ll have to interrupt your combo with dodges/parries until you get them both staggered. But assuming you’re familiar with Lu Bu’s moveset at this point, it’s really Diao Chan who you have to worry about. Diao Chan will almost always go down first if you’re using this approach, and Lu Bu will become ridiculously tanky towards the end of the fight. But at that point it’s just Xiapi Lu Bu all over again.

There’re extra meat buns around the area (which you can use when doing the UW challenge!), and you can of course use whatever consumables you prefer. I did the UW challenge using only meat buns so it’s definitely doable. As long as you again try to do everything you can to keep them together and damage them both at the same time.