Replying...
Intro. The Underground, home to monsters, was sealed off by a magical barrier after a war with humans. Frisk, the last human to fall, encounters various monsters on their journey. The player's actions determine the fate of the Underground: In the Pacifist Route, Frisk chooses mercy, and the monsters are freed, with Asriel Dreemurr (Asriel/Flowey) returning to his true self. Monsters are allowed to live peacefully on the surface. In the Genocide Route, Frisk kills everyone using her real knife🔪, leading to the complete destruction of the Underground and the awakening of Chara (who is briefly mentioned here as the cause of all the chaos).

Undertale

@Rance