Board Thread:Questions and Answers/@comment-29680061-20170613161817/@comment-26543249-20170710060413

Okay, lemme explain it to you:

Frisk is the character you play as in the game in any route; Pacifistic, Neutral, or Genocide. During a Genocide run, Frisk slowly becomes possessed by Chara as he goes on a killing spree in the Underground. At the end, whether the Player agrees or not, Chara destroys the entire reality of the Undertale multiverse.

Chara destroys the universe for one simple reason: Because it wants to and it can.

Chara is a completely separate entity from the Player.