Board Thread:General Discussion/@comment-12190640-20180129033252/@comment-32182236-20180205175655

Chara appears again because they have your SOUL. They're possessing it. Only reason why you can move around Char's SOUL is because Chara lets you. They still take over at the end.

And the initial premise is false. Chara speaks TO the player (we're Frisk, not Chara). You can't ask YOURSELF to hand over your SOUL to yourself, after all. Chara can't be the player. FRISK is a much better candidate for the player, and the stance I take. After all, we do play as them, and we don't see any OneShot-like relationships going on.