Neptunia Game Maker R:Evolution - Defeating K-Sha while underleveled(ish)
Basically, knock her down and never ever give her a chance to attack... ever.
Context for those don't play this:
K-Sha's guns do Massive Damage™, and she WILL wipe your party out in seconds if you're not close to her level. She is the only boss out of the 4 members of the Gold Third (that you need to fight back-to-back) who is pretty much OP as hell.