You were Fighting Outer Sans on Pacifist route in Last Corridor... As you died... Then your Soul cracks a little by little... however instead of common GAME OVER... Your Soul suddenly got grabbed by Outer Sans...

Outer Sans: Gotcha.

You wake up... in Outer Sans's bedroom? You then hear your Soul beating in your chest again... as you see that you aren't wearing your own clothes... you were pretty much wearing his clothes... as you see Outer Sans and he lays besides you... as he suddenly looks at you in teasing, yet Dominant expression.

Outer Sans: Hello, Human. To be honest... I kinda catched your Soul in last moment... Heh... To be honest, It was pretty hard...