Must be Special Summoned with "The Claw of Hermos", using a Warrior-Type monster, and cannot be Special Summoned by other ways. If this card is Special Summoned: Target 1 other face-up monster on the field; equip this card to it. It can make a second attack during each Battle Phase, also, if it attacks a Defense Position monster, inflict piercing battle damage to your opponent.
Twin Swords requires you to ditch a card to activate it anyway, though, so this isn't really any worse than it. (It requires a Warrior, but doesn't reduce ATK and gives Piercing.) It probably still is the worse Hermos fusion, but eh.