Tips to build a Kagero are really nice right now

Tdlr at the bottom vvvv

Well for one it depends on her IVs, if u have +atk or +spd you're perfectly fine, if u have -atk dont bother trying to build her, she wont be able to ORKO units more often, neutral atk is still useable for her. For my Kagero's build, she has +atk -def iv, Luna, L&D 2, Desperation 3, and the sacred seal as atk+1. Now considering i have a +atk kagero Death Blow would be a better skill if Kagero has +atk, that will allow her to one shot most of the entire cast when it comes to infantry. A +spd IV can run the same set although L&D can boost her spd even more and her attack as well, this is where desperation comes in, she is able to ORKO even some horses and Flier units that have decent defences since she wont get the bonus damage from her Poison Dagger+. If you run the L&D(can be swaped with Fury as a budget option) and Desperation build I'd recommend using ardent sacrifice because her defences will be nonexistent, especially Physical defence as she'll have less than 18. Using ardent can safely put her into Desperation range so she can sweep alot of units (as long as she 1 shots them with 1 hit, or 2 shot them with a double+desperation.)
Tdlr: +atk or +spd or neutral on both, no use in -atk/spd for her
A slot: Death blow if +atk L&D/fury if +spd
B slot Desperation if running +spd and L&D
C slot is anything but Threaten Def for 1 shots, threaten spd for double hits.
Example of my Kagero +atk -def if u just want to copy it if you'd like