|Anna's high speed and resistance for an infantry axe user make her an excellent budget counter to the blue, and potentially green, dragons that currently (at time of posting) are ever present in the meta.
Despite lacking any merges, 38 speed is enough to bait and get follow up attacks on many of these dragons, while taking minimal damage in the process - or alternatively, to initiate on them and get kills on the blue ones especially thanks to Triangle Adept 3. Surprisingly, her entire base kit can play pretty well into this build, just needing a suitable A skill to make it work well - however, alternative options of varying investment have been suggested for several other slots to make the build work even better.
Nóatún is chosen as her weapon as a budget choice - it's not the best weapon, but it also costs nothing extra to use and does the job fine. If you're willing to invest slightly more, Slaying Axe+ with a +Res or +Spd refine could be a significant improvement. The faster special cooldown can be exploited with Moonbow or (especially using +Res refine) Iceberg, 5 HP is a nice durability boost, and then you either get: +3 speed, making securing doubles on some faster dragons like Corrin possible, or else +Res, making it easier to fight green dragons. Instead of Slaying Axe+, you can instead opt for another effective weapon such as Slaying Hammer+ or Poleaxe+. These give her a wider niche, meaning more opportunities for her to be useful, but at the cost of being maybe not as effective against dragons, and reducing her already shaky attack against them with no faster specials to compensate.
Reposition is almost always helpful, although it can be substituted for another preferred assist if needed.
Astra is kept as a budget special choice, but Moonbow or Iceberg can be switched in relatively cheaply. Moonbow is nice due to triggering in the first round of combat, helping secure kills she may otherwise miss due to her poor attack. Iceberg works best with a +Res Slaying Axe+ build. Astra is often overlooked and replaced on Anna, but it actually synergises well with her default kit - allowing her to drop to low HP while building the special, and then Vantage killing something blue when you warp in front of an ally using Nóatún. While this isn't exactly an easy combo to pull off, it works better than many people expect.
Triangle Adept 3 helps specialise Anna into dealing with blue dragons extremely effectively. She ends up taking negligible damage outside of specials, while usually doubling and killing them. A more premium option is either Close Def 3 or Warding Stance 3, which also give a significant Res boost against dragons. Warding Breath is even better in theory, but other builds can exploit Warding Breath's special cooldown bonus better than this build.
Vantage 3 is Anna's default B skill, and it works okay. It can combo with Nóatún as mentioned above, or you can replace it with Desperation 3, allowing Anna to get some player phase action after she tanks one or two dragons. This slot is somewhat flexible if you aren't running Astra, though.
Her C slot is fairly flexible. As with most of this budget build, her default Spur Res 3 is fine if you have no specific team goal in mind. Since you'll mostly be deploying Anna against teams with several dragons, the Res Spur will likely be at least helpful.
For her seal, the ones that most help this build are either ones that provide enemy phase defence like Close Def 3. Resistance +3 is also a solid choice, or perhaps Attack +3 to patch up her otherwise shaky attack stat. She doesn't really rely on any seal to work as a budget build option.