Here is the Anna build I'm conceptualizing on.

This is Anna as an arena bonus unit.

Okay first of all, let's consider the fact that Anna has a low attack stat, meaning she's not able to deal any real damage. This build is designed to change that. Because I have a mage in my arena core and this means that this setup is valid.

First off, Noatun gives easy teleportation ability. It may not be a nice niche to have but it can activate multiple effects that foes may not pay attention to.

First off is Sorcery Blade. This is the main skill that offsets her low attack by hitting Res instead of Def, meaning she can do a dent on units like Zelgius (without quickened pulse, otherwise she dies), and only few units have good mixed bulk.

Next if Blue Flame, which is an easy-to-understand skill wherein you just need to be adjacent to an ally to activate its full potential. Pair this with Flashing Blade so that she can activate it every combat (provided she doubles, but this is easy with support)

The rest of the skills are flexible. Wrath can be replaced with Renewal as she will be expected to trade hits. A dual spur is useful for helping allies.