Description
To put some context into this:
After Anne ran away from the lab that one night and met up with new people around Snowdin, W.D. Gater was still lurking around. More specifically in their mind. He was able to work on a serum that would inhabit and take control over Anne's mind and body. Making them do whatever he pleases to do to them.
In this image, he forced Anne to go on a genocide run and kill all of their friends. Because if what Anne has cannot be killed (their soul) then he would have to hurt the things that are the most important to them.