Adamant

The four royals prepared to meet the Voidreaper.

The plan was simple and straightforward.

There was no need to complicate it.

Divulge their identity.

Acquire the body.

Kill the Voidreaper.

There were sixteen Martial Masters. 

Against a single Martial Senior.

Yes, he was an extraordinary assassin. They could all honestly admit that he was probably the best Senior-level assassin that they had ever come across. In fact, they felt silly hiring anybody else except the Voidreaper.

Had they hired the Voidreaper alone, he would probably have succeeded with his extraordinary, almost God-like ability to snuff life and bestow death. Sierra had been exactly on the mark when she said he was too good to be excluded due to his condition to learn their identities. Had they not hired him, Rui Quarrier would have escaped and gone to the Martial Union.