It's a series of AUs that sort of organically formed over on Twitter, basically reframing the way Izzy's dedicated his life to Edward, and what it might look like if Izzy had had cause to devote himself to someone other than Ed. The most common ones I've seen are Hornigold's Izzy, Mary's Izzy, Stede's Izzy and Jack's Izzy, but there's been lots of fun variations (believe someone did Evelyn's Izzy, and there was a lovely one of an Izzy who belonged to the sea). There's also a throughline of someone sort of handwavey interdimensional travel stuff, so that either all these different Izzys keep popping up on the Revenge and have to get sent back to their proper timeline, or the Revenge itself is dimension-hopping and visiting these other timelines.

I'm not sure who exactly came up with the Izzyverse idea over on Twitter, but I was struck by the concept of Mary's Izzy, who definitely killed his universe's Stede for her

Realised that I somehow managed to miss this one in my posting blitz here, have an Izzy :)

https://archiveofourown.org/works/43245189

https://archiveofourown.org/works/42513585

Full nsfw here: https://i.imgur.com/KdVZROF.jpg

Full nsfw here: https://i.imgur.com/9PVWJCt.jpg

https://archiveofourown.org/works/42948366/chapters/107903619