|Like most Tharja builds, this build focuses around her default Rauðrblade+ as well as Desperation 3 (although there are alternatives recommended if Desperation is not available), but with a few cheaper alternatives compared to her optimal set.
Her assist is either Draw Back or Reposition as having a positioning skill to move around her teammates in and out of danger never hurts.
Moonbow is her special of choice because of its low cooldown. Additionally, because her weapon Rauðrblade+ increases special cooldowns by 1, other specials become notably lengthier to charge up as well (such as her 3-charge skill Vengeance now being 4 charges).
We keep her default Darting Blow 3, as while she does lose out on the punch of some extra stats, the extra Spd can help her double more units as well if need be. Fury 3, if available, is a more solid option though as it gives her both Atk and Spd she can use to hit harder as well as defensive stats that don't hurt either. Fury can also be used to activate Desperation if necessary.
As mentioned, her B-slot passive is Desperation 3 as it allows her to attack twice consecutively when she's below an HP threshold against enemies she can double. This synergizes with Darting Blow, which provides her more Spd to double, as well as Fury which provides both stats and has HP drain which can help push Tharja into Desperation range. (This is the reasoning behind why both of these are recommended for her A-slot).
If Desperation is not available though, a breaker can also be chosen to more definitively check a subset of heroes such as Swordbreaker 3 at the expense of having a more specialized of a role (but by no means a completely terrible choice if it's the only available option).
Her C-slot passive is flexible and should be selected based on team needs. While most teams might prefer an Atk or Spd buff of some sort, her default Spur Res 3 can also work fine if on a budget or if her other team members are more defensively bait-oriented.
Her seal should be either Speed +1 or Attack +1. The former gives her more Spd to potentially double even more units while the latter might be preferred if a player finds Tharja lacking some punch (especially if Darting Blow is selected as her A passive).
It should be noted that since this is a Rauðrblade+ set, Tharja needs a dedicated buff support teammate to provide her buffs in order to shine best (eg. Eirika, Ephraim) as not having a buff support reduces her damage output and potential drastically.