Afraid

Everything is as it should be in the world of Underswap, especially for Sans, until one fateful day where Papyrus begins to tread a dark path. After becoming addicted to alcohol-spiked honey, Papyrus begins to change for the worse and abuses Sans in many ways. Sans wants to change his brother to get him back to normal, but at the rate things are going it seems impossible. Believing the best in Papyrus, Sans stats by his side, enduring his horrendous abuse and terrible habits in the hopes of helping him...but just how much can he do for him, and what will it cost his soul?

~~~

This story contains every mature theme I can think of.