Black Dot
Ailsa felt her heart clench when she saw Ryu. Though they seemed to have been taking things lightly, there was no doubt in either of their minds how important this matter was. If Ryu lost, not only would he lose Ailsa, but he might very well lose his life.
He didn't know the process or what it was entail to separate Ailsa's Fate from his own, but as the wielder of the Mysteries of Heaven and Earth Pupils, Ryu had a comprehension of Fate most didn't have.
If the Cultus Clan wanted to save Ailsa, it would require one of them to sacrifice. And, the choice for who was obvious.
The best case scenario after such a separation would be Ryu losing his talent and ability to cultivate. The worst case scenario would be him losing his life entirely.
To Ryu, though, both of these scenarios were a death sentence to him.