Mysteries of Heaven and Earth
Ryu's eyes narrowed, but he didn't respond. This much should have been obvious, no? If not for this, they wouldn't be making all of these moves.
The reason why Ryu killed himself in his first life was because he sensed the shifting of Fate. As for what triggered him to look into such a thing when he never did, it was the conversation he had with Elena on Shrine Mountain the day of his thousandth birthday.
Back then, Elena had mentioned that her Holy Wing Clan had gained as many as nine Holy Wing Saintesses in the last several thousand years. The moment he had heard this, Ryu knew that this number was far too large for it to be a simple coincidence.
The births of such talents require a large amount of Fate. If it was just one extra, it could be passed off with a shrug. But, to have nine in the span where having even one would look like a great boon was absolutely ridiculous.