WindsongBuild and Guide

Windsong is a 6-star Arcanist of the Star Afflatus. She is an incredibly high burst damage Crit oriented character. 

Her main Incantation is technically "Rehabilitation", it's what you'll attempt to stack in your hand and it's individual casts are what her Ultimate, "Long Long Journey", casts all at once. This Incantation's damage is increased through the spending of [Eureka], gained though casting her Incantations. 

Her other Incantation, "Practicability" is used to generate "Rehabilitation", as it grants Windsong stacks of [Preparation - Windsong] that are consumed at the start of the round to generate an amount of her cards. Not only that, when "Long Long Journey" is cast, all "Practicability" Incantations in hand are transformed into "Rehabilitation" ones, further increasing her fuel. 

As told before, "Long Long Journey", casts all "Rehabilitation" Incantations in your hand at once. However, first it applies [Confusion] to the target, then it grants [Eureka] to Windsong and prevents [Eureka] from being consumed that turn, and for every stack of [Eureka] Windsong gains a stack of [Measure] (also granted by her Insights whenever an ally crits or inflicts [Confusion]) that increases her Crit Rate and DMG. 

Gameplay:

1. Pull "Rehabilitation" Incantations

2. Ult

3. ????

4. Everything's dead

Oversimplified as that sequence is, that is pretty much what happens. Of course, there is nuance to this; I'd argue that Windsong is probably one of the hardest characters to play when compared to her peers. To make the most of her, you need to think about your card management, maximize the cards generated through [Preparation] and slowly build your hand to consist of as much Rank 3 "Rehabilitation" Incantations as possible to unleash with "Long Long Journey". 

But that's all you have to pay attention to. Her self-applied [Confusion] and the stacks of [Measure] she gains, on top of her other Insights, all but guarantee that she at least critically strikes most of her attacks, and unlike Spathodea, she doesn't have to actively interact with her own kit to maximize her Crit Rate. This is great because it opens up a lot of options in terms Supports to pair her with: Vila is of course great for her Moxie/Eureka and Crit buffs but other characters like 6, Necrologist, 37, Voyager, Twins Sleep, and later on with Semmelweis, Mercuria and Kakania, there are very few characters she doesn't play nice with. 

And that's because she is ultimately a very simple gal. She hits Ult, things die. The difficulty lies not in the mechanics of her kit but the player optimization of it, and with the new Tuning releasing with the patch 1.9 anniversary even that part is dumbed down, earning her her top spot among the damage dealers.