In most cases, it is legal to watch fanfiction. Fanfiction is generally considered a form of derivative work based on existing intellectual properties. As long as it's not being sold without permission or used in a way that violates copyright in a major way, just reading or watching it for personal enjoyment is usually okay.
Fanfiction.net could also be a place to check. It has been around for a long time and hosts a vast amount of fan - made stories. However, the interface might not be as modern as some other sites. But still, it's worth a shot to search for your desired Dante vs Bayonetta fanfiction.
Makima's fate in the manga is quite complex and involves a series of dramatic events. She faces powerful opponents and has her own agenda that leads to significant developments.
Well, Makima's death in the manga is the result of a series of events and confrontations. It's not straightforward and is tied to various character interactions and plot twists.