Low throw them if you expect it. It's the same against any character with good TC moves that you expect spammed, 2A+G_B+G become interrupts you can throw out at low disadvantage. If you're afraid of the throws do a lot of moves that push out on block: B, 33B, 44B, 3K, 22B, 66A, 4B+K, 4[A], A(~)B. That way you won't have to deal with mix-up as often.
Otherwise be careful, asta is kinda weak to his own step.
i tend to step a lot at mid-far range and bait for whiffs on asta vs asta. its a pretty strange fight (as all mirror matches are imo). once they/im in i tend to step it up on aggresion as you cant effectively space asta vs asta at closer ranges.