[OP17-117] - Maser Saber (The World's Strongest Warriors)

When my opponent trashes cards with this [Trigger] effect, which player makes the choice?

The opponent of the player who activated this [Trigger] chooses whether to trash 3 cards from their own hand or do nothing. If the opponent does not trash 3 cards from their hand as a result, the player who activated this [Trigger] KOs up to 1 of their opponent's Characters with a cost of 6 or less.