Brash Assault Seal

Yep, Desperation+Brash Assault is an amazing combo. Any slow brave weapon user benefits from this because it gives you a guaranteed quad when below 50% hp. I used to run it on my Cherche and my Frederick, but there are countless options that work well with it.

And the best part? You only need Desperation 2 to make the full combo work.

I also use it on Cherche, and she ORKO's almost anything when below 50%. Basically, any High Attack, low speed unit benefits from this the most, as they can not double naturally.

Keep in mind that some bulk is required to survive a hit, and get below 50%.

Any Brave user works well

As the above have said, brave users use it very well but Anna also uses it well. When she gets below 40% health her axe's Escape Route 2 activates, Desperation in her B slot and Brash Assault seal let her warp around to her allies and double enemies regardless of their speed. Brave users are certainly the best but if you're reduced to using Anna as your arena bonus unit bear this in mind.