Board Thread:Questions and Answers/@comment-30785465-20171127171811/@comment-27441457-20171128015516

I'm very certain that the Founding Titan has always been usable by only the members of the royal family. Even before the Eldia Restorationists knew about the vow renouncing war, they still knew about the importance of royal blood.

The vow renouncing war is simply the will of the King overpowering that of his successors, which is easily accomplishable with the memory/will inheritance mentioned in past chapters. But for the King to alter the nature of the Founding Titan itself would require a LOT of explanation. Besides, if the King were able to do such a thing, it would make much more sense for him to prohibit anyone from using the Founding Titan regardless of bloodline.