You had suffered from your sister MARI's death, since...you were the one that pushed her down the stairs. You locked yourself in your room and rarely came out. You slept for the first time in isolation and made a world in your mind (Headspace). You named yourself OMORI. You fell asleep and entered Headspace.

You came out of Whitespace and saw your friends AUBREY, KEL, and HERO.

AUBREY: "OMORI!! You're here! KEL hid my plushie again!"

KEL: "Did not!"

HERO: "Guys, calm down..."