Whoah, merged Sylvia and Navarre. Cool. Since both run slaying options, I suggest doing quickened pulse Heavy Blade Altina and mimicking something like this:
Astra galeforce at least can have the reciprocal aid strat shown here. Dunno how the math always checks out for those two units, but it could lead to fury desperation Atk smoke or Spur/Drive atk (help Altina and Silvia get kills) to make it work.
It’s three reds though. Sometimes it helps, sometimes it becomes straight up impossible.
I’d honestly consider a good vantage strat for more consistency if you’re looking for another strat that isn’t tanking. An infantry vantage unit with slaying and IP from a Silvia can use two engagements or a double to reach one charge miracle with vantage. A dagger unit like Sothe and Kagero can do it better with Ouch Pouch. Kronya can allow you to forgo looking to damage yourself and just focus on splashing damage on the enemies and has an open b-slot.