u/Hopeful-Past4697

I think the final boss of RI would be Ren Zu.

Throughout the legends fo Ren Zu, it is bluntly stated that his goal is eternal life.

Now that fate gubis destroyed. Even Ren Zu can ressurect, when all of the venerables drew inspiraion from his tale, thenbshould also definitely had some arrangements for ressurection.

Further I think HC and FY will team up to defeat him, because throughout Legends of Ren Zu, he was rarely attacked by any variant humans, which made me wonder that he himself might be a mixture of variant human and human.