Ruling

I control 1 Wind-Up Zenmaines with two Xyz materials, 1 Leviair with 1 Xyz material, 1 Gachi Gachi with two Xyz materials and a Geo Genex, backrow is Torrential. My opponent summons three Six-Samurai monsters, I activate Torrential, opponent chains Six Style - Dual Wield, targeting Torrential and one more card. Can my opponent do that? What happens?

Your opponent can't use Dual Wield because they had more than 1 Six Samurai monster on the field at the time.

Nebuwah wrote:Your opponent can't use Dual Wield because they had more than 1 Six Samurai monster on the field at the time.

Okay, but what would happen if he had only 2?

The card text says "activate only if the only monster you control is 1 six samurai monster" so if he controlled any other monsters at the time he could not have activated it because he could only use it with 1 and only 1 Six samurai monster on his field.

He can only use it if he controls ONLY 1 face-up ATK positional Six Samurai:
'Activate only if the only monster you control is 1 "Six Samurai" monster in face-up Attack Position.'

LuzCeleste wrote:The card text says "activate only if the only monster you control is 1 six samurai monster" so if he controlled any other monsters at the time he could not have activated it because he could only use it with 1 and only 1 Six samurai monster on his field.

Ok, thanks for clearing that up.

And, for the record, if he activates it (having ONLY one six sam face up on field) and targets the torrential you activated, then torrential still resolves and goes to grave.

The condition for Six Style - Dual Wield is pretty harsh, the only 1 monster you control must be 1 "Six Samurai" monster in ATK position in order to activate it, so in this situation, activate Six Style - Dual Wield is an illegal action.