xDONEbyMADDIEx
This story takes place after frisk breaks the barrier and sets all monsters free, but the monsters don't know frisk as a human but as teen skeleton. The only ones that knew frisk was half human half monster are Muffet, Chara, Asriel/Flowey (flowey is no more as he is back in his normal body) Toriel and Asgore. Frisk is half monster, half human in this story and all underfell characters except for Grillby, Asgore, Gaster, Muffet, and Toriel are teens attending school.
When frisk broke the barrier, they parted ways after frisk told them that she's their ambassador (one that looks after them) and to always treat humans kindly like she had shown them.
Momsters living peacefully with humans again....
In this story, sans looks and tries to find the skeleton that freed them called frisk, as he is in love with her however he still hates humans and what he doesn't know is that she's human and closer then what he thinks....