Kagero Build

Reprisal increases your damage output by 30% based on how much HP you lost when you activate it.

Moonbow is the same as Luna but has a shorter (2 turn charge timer compared to 3 from Luna) cooldown while being slightly weaker in power (Moonbow Ignores 30% of the opponents def/res while Luna ignore's 50% of their def/res)

Moonbow is obviously preferred over Reprisal on Kagero, her abysmal HP stat cannot abuse this ability much like Karel can. Moonbow is needed in case Kagero finds herself in combat against anything that is not an infantry unit.

One point to note is that while Luna does not activate as often, it nets more OHKO which Kagero sometimes comes to rely on, depending on what A and B skills you run.