Theorycraft : Tana, the steady flow

♪ She has the flow, she gives the blow,
She is the one who decides the rythme of the battle, her armor doesn't rattle,
Nobody can flaw that pace, on a pegasus - never leaving a trace~ ♫

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TANA
IVs : +Spd / -Hp
W: Vidofnir
Sp: Aether
A: Close Def 3
B: Windsweep 3
C: Guidance 3
S: Close Def 3

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The idea behind this skill set is to capitalize on Tana 's stat spread (especially Spd and usable Def/Res) as well as her weapon, Vidofnir, providing her an flawless defense against melee units.

In fact, she has the highest Spd stat (39 boon'ed) among all melee unit excluding sword users which aren't a threat anyways due to the triangle advantage.

However, one may argue that other units will boost their Spd stat even further with Fury, Life and Death and other a-skill or sacred seal that Tana decides to give up on for more defensive potential. It's true but it won't enable them to take Tana down actually. Only Raven (Fury+Spd seal) and some lance users can reach 44+ Spd to double Tana but she should able to deal with them in most cases anyways since she has 44 Def and the ennemy either suffer Fury's recoil or LnD's bulk penalty to reach that high Spd.

Another con-argument could be weapon inherance, which is in fact endangering Tana's top tier Spd position. There is no answer to that except the fact that you can use it on Tana as well, as an alternative to Vidofnir's specialized melee defenses.

Berkut Lance++ (+Spd) would provide Tana 7 more res on defenses, which will help Tana against any source of magic danger, plus she should be enough to resist Reinhardt on equal level of buffs.

Carrot Lance++ (+Spd) which is also a very good option here for once, since Windsweep makes the duels longer (prevent both follow-up on initiation and foe's counter-attack). Thus, Tana should regenerate a fair amount of Hp in between the engagements.

The real advantage of going for a refined inheritable weapon over Vidofnir is that Tana would benefit greatly from these 3 extra Spd points both against regular weapon users and refined weapon users (maintening her top tier Spd position). Plus she also benefits greatly from the 5 extra HP of those and the effects explained above.

Now, let's speak about skills alternative :

A-skill : Close Def 3 is prefered due to the majority of melee characters both in the arena at higher tier (due to their higher BST) and in the PvE part of the game (since the number of melee units >>> ranged units) so it would actually benefit the PvE situations where ennemies are randomly generated (i.e. Tempest Trials).
However, this skill can be swaped for Warding Stance or Distant Def 3 if one wish to tank mages more easily. But it won't help much against the archers (weapon effectiveness), the ninjas and the clerics who are now using massive indirect damage (Pain+, Deathly dagger, Poison Strike, Savage Blow...). For the latter reason, Steady Stance is an inferior option to Close Def 3 but Steady Breath can be choose if one can afford it, it has its pros and cons too but Close Def 3 is globally just as good if not better.

Sacred Seal : Same as above concerning Close Def VS Distant Def, except that here Spd+3 seal and Phantom seal are two additional options, which would indeed be effective especially if one decide to stick with Vidofnir, since it would answer the Spd powercreep (brought by the weapon refinery) by changing the original build BUT reducing its purpose overall effectiveness.

C-skill : Guidance 3 is chosen here, since Tana can totally be integrated in a mixed type team with this skill set, where Guidance 3 provide a great amount of mobility for the team. This is especially true since Tana is supposingly a super melee tank in this case, which enable her to work as a highway for her teammates.
Of course, the flyer buffs/bonus will be prefered in a flyer team, in order to create that flyer emblem synergy. Other C-skills are also possible since it mostly depend on the team in its globality so the choice is yours.

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That's it, today with the increased specialization of every units due to all these new skills, seals and the weapon refinery, it feels off to give a build without alternative to adjust different needs and situations.

Thus, the build in this theorycraft is more like "a core" or "the base" of the idea behind what's possible to do with Tana and her unique features and the keys to adjust it against the threat you may encouter.

I believe her best bet is actually to use Berkut Lance++ over Vidofnir since the Hp, Spd and Res actually improve both her effectiveness at using the build and her versatility (at tanking mages). Then for the skills, I would stick with a double Close Def 3 to keep her specialized enough.

Thank you for reading, hopefully you liked the idea and all.