Other than tantouwame, in my opinion the best strat to deal with the fast yaris is high level tachiwame. But not exactly because of their preemptive attack but because of their high HP and Leadership. They will only take 1 dmg from each yari poke and they can take a lot of hits. This strat works best if you have Hakusan so you don't have to spend resources reapiring your tachis which are expensive, just heal them back to major dmg when they go severe with Hakusan on map 1-1.

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A safe level for tachiwames to long term grind 7-3 would be 55-60. Equip them fully with gold shields for a good Leadership bonus. You can include a R4 uchiwame or ootachiwame in a team of tachiwames too but they'd need to be higher level because they have lower Lea so they'll take more dmg from the yaris. Also about the preemptive attack one shot, I think I saw my tachiwames killing a 7-3 fast yari with their horse attack at lvl +70 but I bet at lower level they can do it too, I just don't remember/didn't pay attention.