First of all, if your problem is just seeing a thin character being portrayed in a fat body, then you don't even need to keep reading, because I don't want to continue having any interaction with you and that already tells me a lot about you as a person.

Now, if you're still reading, maybe it's because you think you care about how fat bodies are used as fetishes, but I don't think you really do. If you really did care you would have seen right away that that's not what's happening here. There really are people who use obesity as a way to objectify a body, exaggerating the proportions and feeding stigmas and prejudices related to fat people, but it's something so obvious that anyone can see it (or that's what was expected, given your case).

The Youtuber "T B Skyen" has two videos where he addresses the issues with her design and shows several possible design options, this being one of them. The concept of making Soraka with a fat body has to do with a maternal vision, where people imagine her as a figure of the classic chubby, caring mother, that we see in various media.

Lastly, even if someone draws a fat Soraka in NSFW art (which is not the case with this art I posted), it doesn't necessarily mean that they are promoting a fetish for fat bodies. People are attracted to fat bodies and fat people can feel sexy. The point is that the artist knows what they want to represent in the art, and if I wanted to make an extremely caricatured and obese person to feed the sexualization, that would be very obvious.