Board Thread:General Discussion/@comment-26006155-20181123023529/@comment-32182236-20181123172732

"Well, that's just it. When Flowey is talking to us at the end of the Genocide route... Flowey IS talking to Chara. She's already taken over 99% of Frisk.

It's only in the True Pacifist Ending, where Frisk is been perfectly good and is 0% possessed by Chara, that Asriel finally realizes that Frisk is a different person, and not their old friend at all. Because in that timeline.. we're still Frisk."

In Asriel's battle he calls us Chara until realising we're not. This is before Asriel's battle, so he's still under the illusion that we're Chara. So Asriel thought he was talking to Chara then, even though he wasn't.

And I brought up the Genocide Route specifically because he was able to chance his voice to fit Kid Asriel's voice in those last moments. Thus, the Elevator Man's voice being Asriel, even as he's still Flowey, isn't all that far-fetched after all.