Remember that the power of your soul can be destructive or creative and the choice is always yours. In the game, you will definitely feel the connection between the destiny of the entire world and your personal decisions. Chara was an evil child and wanted the entire universe to die, so when she controls Frisk, he behaves violently and Chara finally gets what she wants. It is suggested that when Frisk becomes violent and starts killing monsters, this is not his authentic personality, but he is being possessed by Chara, the first kid who came to the Underworld. In case you choose Genocide as your route, you will fight Sans as the main boss when the game will approach to the end. In case the player follows the Pacific way, Sans and other peaceful demons will start helping him and claim that he is the kind person with a warm heart.
In the demo, Flowey and Chara have the ability to change the game's instruction manual based on the course of events the player takes. With time, your route will shape according to the actions you choose – Pacific, Neutral, or Genocide. This feature doesn't exist in the final game: given the nature of EXP in the game, the demo's behavior wouldn't make sense and could unfairly lock an unsuspecting player out of the best ending.
In case you start attacking, they will stab back. You can become friends with the demons if you decide to talk to them. When meeting the demons, he/she can behave differently: start a fight, stay neutral, or deal with them in a friendly and peaceful manner. As for the paths to follow, the play the main role in the game and decide the destiny of the world you appeared in (and your own, of course). However, depending on the route he chooses, their attitude will change – those that are pacifistic will support and help him, while the evil ones will be frustrated in case he chooses the nonviolent path and vice versa. He meets monsters on his way and they all treat him differently. Frisk is the eighth human being that accidentally made his way to another world. He gets there accidentally after falling down from a magical mountain Ebott and rolling under the ground. Everything starts when Frisk, or a Human Child, appears in the world of the Undertale.