Best A skill for +Att -res Kagero?

I'd go for lnd personally, since she didn't have much devensive capabilites to begin with and doubling the opponent definitely helps her in securing the kill, especially with her weapon's low might

LnD seems like the best option for her. Maybe use vantage to mitigate the loss of defensive skills.

I had LnD 2 but I switched to close counter because she very rarely needs to double to obliterate infantry units. She can wreck a whole team.