Once per turn: You can target 1 Set Spell/Trap Card; destroy that target. You must control another "Six Samurai" monster with a different name to activate and to resolve this effect. This monster cannot declare an attack during the turn this effect is used. If this card would be destroyed, you can destroy another face-up "Six Samurai" monster you control instead.
Rulings for The Six Samurai - YaichiYu-gi-oh! Card
The first effect of "Yaichi" targets the card to be destroyed.
If the targeted face-down card is chained to the activation of this effect, it will not be destroyed because it is face-up when the effect resolves.
If all other "Six Samurai" monsters you controlled were destroyed by an effect chained to "Yaichi's" effect, "Yaichi's" effect will not resolve.
If "Yaichi" declares an attack, then is flipped face-down, then flipped face-up, you cannot use its effect that same turn because it already attacked.
If "Yaichi's" effect is used, then "Skill Drain" is activated later, "Yaichi" still cannot declare an attack that turn.
Please see "The Six Samurai - Irou" for additional rulings.