Four
Ryu felt as though his very spirit itself was being crushed.
Going through an Extinction was like expunging all of your accumulation at once. It wasn't a physical struggle, but it could manifest as such as the strength of the body was being forcefully torn apart.
To undergo an Extinction was to force one to question their very existence. Every aspect of your being would be assaulted and ground to dust, then amidst all of that pain and right in the middle of what was essentially an existential crisis, you would have to build yourself up again.
For Ryu who had brought his Inheritances to perfection first before doing anything, the process was incredibly painful. In addition, because he was older than the optimal age, his mind also lacked the same sort of placidity that would have made the situation easier.