One Day, I'll Save Myself- Reincarnated as Sans

You remember a life before war. A life lived in a body of flesh instead of porcelain bones. You look down at your little brother, little precious Papyrus, swaddled in green. You know then and there that in the first time since you were forcefully created and pulled into this strange vessel, there was something more precious than the stars themselves. And you love. And you fear. Because you'd even go against your SOUL to protect Papyrus, even if it meant selling yourself to the person you hate most.

The lengths an older sister goes through to ensure her little brother survives the HP Hell that is a transcontinental war.

Second Part:

Three years after the end of the war, you've finally done almost everything you promised to do. Before you could fulfill the last promise you make, you and your brother, Papyrus gets forcibly displaced into an alternate universe. It's like a graveyard in here with all of these skeletons, and your previous life's mother was right when she told you to never leave a light on, unattended.

Third Part:

Getting a glimpse of hope in your efforts to return home, you and Clover discover the perils of rushing the process. It seems you are Odysseus, and home is a long ways away.

But Odysseus didn't have to deal with SOUL-less parasites and alternate versions of himself that are a couple crackers short of common sense. You are... the ultimate mother hen.

TLDR: OC (technically a reader-insert) gets reincarnated as Sans in wartime and wants very much off this ride. Will turn into a machine-induced universe travel fic, but you can just cut it off before that. Will use SHE/HER/HERS in terms of pronouns.

A tribute to my older sister who has really gone through some stuff to keep us fed and loved.

Disclaimer: Undertale belongs to Toby Fox and I have very limited understanding of the other AU's in the Undertale fandom.