Welcome to the lords with high defense getting -Def club. In my case, Chrom. Same boon too.
Anyway, niche build incoming! Since Tyrfing has a built-in Defiant Defense 1.5 -- Defiant Def 2 gives +5 defense instead of 4 like Tyrfing --, it can meld well with Brash Assault which requires you to be <= 50% HP. Also, Defiant Defense actually stacks with Tyrfing meaning he can have +11 defense when he's in their range. Ideally, you'd want a +Def Seliph so his defense can be as high as possible, but you can also hope for another one if you really want to use Seliph and this gimmicky build. Here's a post about it:
https://serenesforest.net/forums/in...d-here-thread/&do=findComment&comment=4814262.
Lyn is arguably the best user of Brash Assault because of Sol Katti's innate Desperation 3. Below her, I think it would be 5* Alfonse and 5* Seliph because of their swords having innate Defiant Attack 2 and Defense 1.5, respectively. Seliph would require less work since he'd just need to inherit 2 sets of skills and no feathers if you summon him as a 5* while Alfonse has to work his way up from 2* which does allow him to get a ton of SP, but it's Alfonse -- nobody uses him.
Post about Alfonse as a Brash Assault user:
https://serenesforest.net/forums/in...efore-posting/&do=findComment&comment=4811047.
Anyway, below them, it would be Bartre and Hinata who come with the skills by default, so no real work to be done their and they have the highest defenses compared to the others, especially Lyn. That said, because they don't have legendary weapons, they could fall behind. And right below them would be 4* Seliph and 4*-below Alfonse since while they have the stats to use it, they don't have their legendary weapons and you have to give them Brash Assault. Others would be people like Chrom and whatever slow and tanky units.
Brash Assault is really niche. Quick Riposte is better and safer since you're using it in the "green", but has a lower range. -breaker skills are specific, but have a large range and prevent follow-ups. Brash Assault forces you to be in the red and as the ideal users are tanky and slow, they risk getting doubled to death even when they can use Brash Assault. Also, it doesn't work against units who can't counter them. So, for example, you can't use it to burst down a mage by deliberately taking damage. Desperation just requires that you can double anyway which means if you can double someone, then they're dead regardless if they can hit back or not. But hey, if you have a ton of spare Bartres lying around, then you can make them useful by giving Brash Assault away. Or Fury... Or Smite... Or a Hammer.
Also, speaking of stuff stacking, Death Blow does stack with Durandal's Death Blow 2 meaning you can get +10 attack if you initiate combat:
https://serenesforest.net/forums/in...ion-and-links/&do=findComment&comment=4820281. And then there's the whole Renewal stacks with Falchion's innate Renewal 2, so you can make them into ghetto healers with Ardent Sacrifice or Reciprocal Aid.