Lyn Brash assault + Desperation + Vantage ?

"Unit automatically makes a follow-up when at HP ≤ 50% and attacking a foe that can counter."

BA only works on initiation.

Not 100% sure, but last I checked BA only works on initiation, so it wouldn't synergize with Vantage in particular. If you specifically want to abuse the effect of Sol Katti, Wrath 3+Moonbow synergizes best (get Neph while she's a focus~). Next might be Escape Route for warp shenanigans to choose your battles perfectly, only problem is the lower HP threshold.

I slapped Wrath onto my own Lyn. Vantage doesn't synergize with Sol Katti at all. Vantage should be used on units that can counterattack at any distance like Hector, Takumi, Ryoma, Camus, etc.