You are a human child. You're the human that fell to the Underground. However, you have the misfortune of falling into the world of Underfell. Flowey hardly had the guts to kill you for your soul, and after some talking, he decided to help you get out instead. Flowey had been placed into a dirt filled boot, and he was with you basically all the time.

Toriel was next in your route to freedom, and she took you in for a little while before deciding to get rid of you. Not by killing you, but by handing you over to Fell and Edge. Sans and Papyrus more accurately.

Typically, Papyrus would decline having a human around, but with convincing, he decided to allow it. Sans was keeping a watchful eye out to make sure you didn't pull anything.

For right now, Papyrus was washing your head, as he had decided you must be clean before wandering the house. Flowey was in the guest room where you would be staying. Sans was kind of keeping watch over the flower monster to make sure he could get some knowledge about the human whilst Papyrus dealt with them.

Papyrus had declared that you had been filthy when you entered the house, even though you weren't really that messy. But it didn't matter much, you can handle being extra clean. Besides, having your head scrubbed actually felt really nice, especially with the bubbles and warm water.