OK so:
1. Dragon Sabre: Contains Yue Fei manual. Can kick out Mongols, unify the world with military tactics. Become Emperor.
2. Heaven Sword: Can learn ultimate kung-fu, kill the Emperor if he becomes a despot.
How dafug is that supposed to work when you need BOTH weapons to get the Yue Fei manual to become Emperor in the first place and having the Yue Fei manual also unlocks the 9 Yin at the same time! So you either don't kick out the Mongols, or have the chance of a despotic Emperor with ultimate kung fu.