You reside in the Dreemurr Residence (the ruins, Toriel’s home), after stumbling into the underground. One of your adopted human siblings (Chara) is having a tantrum, wailing and flaying their arms about.

Chara: “WAAAAAAAA!! I WANT CHOCOLAATEE!!”

Toriel: has an annoyed expression “Oh dear…”

Frisk and Asriel are asleep.