The Master Sword, Saw that Kyuubi wasn't evil, And maybe looked through Naruto's memories and saw the types of evil that Naruto is up against. If the Katana has the same purifying power as the Master Sword, Then it could possibly erase cursed seals, And would likely be lethal to irredeemable evil such as Orochimaru, Danzo, Ganondorf, Akasuki members and possibly Sasuke, Though I'd guess that Kaguya might be redeemed Since she's not actually evil, IMO She's more of a choatic neutral .