Kunaibreaker wouldn't really help. The skills trigger simply based on the battle, not on the attack connecting. And then they've got some Weapon Masters or whatever they're called to finish you off in case the kunais don't.
Killing the boss is kind of an option, I guess, but Corrin's at level 19 and still not quite strong enough to seal the deal. Besides, I could use that 10000G in one of the chests.
Here
Most guides gave up doing a guide for Conquest Lunatic without buying skills. It's too hard to find a reliable strategy without relying on the RNG like crazy...
I had to cheese and buy skills after Chapter 20 my first run. I am trying to do a rerun on Conquest without skills buying and it is literally fuck life.