Toki.
She was apparently that chick who came from 800 years ago, with time powers and shit... with a resume like that, we expected her to be special, and give us info bombs and shit.. how Wano came to be, clues of what happened to the void century back then, etc... but nothing..
She came from the void century, yet revealed nothing about it... and apparently died, like any ordinary flashback character, with nothing to reveal, even though she came from 800 years ago... I mean, what happened to that? And hell, instead of Toki, it was Oden who came up with that 20 years thing...