Tana Building

I dont have a lot of time right now to help you
but

if you have Close Defense from Summer Tiki, that skill combined with Vidofnir gives your Tana 42 defense

Neutral Def Tana can tank pretty decently, but the problem is her HP is on the lower side to be going for that- and even more-so in -HP.

Take it you want her to be able to kill reliably, as well? The same as advice I gave to a ton of people is to have her on Fury. It's just an all-around boost that works on both ends (offense and defense). Granted, it's not like you'll be prolonging matches (which is why at least two Reposition team mates are recommended). For a B skill, either Swordbreaker or Desperation work.

A: Fury
B: Desperation
C: whatever

Keep Moonbow.

If you have the +1 Spd Seal give it to her for the round 40, otherwise give her Quickened Pulse or +1 Atk.

Desperation aids her durability by attacking before they do.

This is how I build her! Yup do the math she will get 42 defense in the enemy turn which is kinda insane with her already high atk and speed stat. I do some Arena Assault with her and she can sulk up to even with brave weapon and became a phenomenal support unit in the enemy phase