I've seen the comments below or above, i have the same concept, same story kinda, but different characters but still similar to the original
For example, instead of toriel, there's grown up version of Asriel, and instead of Undyne, theres this dude called the "Saviour".
And instead of Asgore there's Gaster, everything is changed but still similar to undertale, if ya wanna know more tell me.
Btw, here, when you spare (in this case) Asriel, the lets you go, but if after you complete the equivalent of snowdin, and go back, you'll find on the kitchen table a glass container with a monster soul, its small, the container i mean, so you can pick it up, which is needed for a true pacifist run.
Anyways, if on a genocide run, when ya get to The Saviour, its gonna he hella hard.
Plus i got something from deltarune and added a cool secret boss only accessible in a geno, the secret boss has way too many Phases and way too many mechanics, he is called " The Devourer of Souls" once you actually kill him, he drops a special item that gives you +15 defense and +20 attack, plus +25HP