I'm going to quickly explain this and the structure of this AU.

Basically, Gaster commited a crime similar to Interracial marriage. He had three children with a fire-wolf hybrid. He knew the hybrid would be excuted, but he paid for his children to live.

Emily was just old enough (8 humans years old) to watch this happen. She asked Gaster why he allowed this to happen but Gaster never gave her an answer. She grew up seeing the Hybrids be treated like dirt. She hated that she was a "Beta Hybrid" and she had to watch this happen.

She had to raise Jeremy since Gaster only took Bellona under his wing. She hated him, but knew he was the closest she was going to get to Asgore. She met Zoey, Chara, Asriel, and Frisk at her highschool since she is currently a senior.

Zoey and the royal trio thought Emily was right and wanted to support her in any way.