It's a very nerdy one.
In Final Fantasy XIV, there's a race of little dudes named Lalafell. Their naming scheme makes for repeated and rhyming couples between the first and last name.
I made a Lalafell boy years ago named Cocozan Cozan.
After playing for a bit, my wife's character and mine got married. I decided to change my character's last name to hers, so the Cozan was gone. We always joked about the height difference, though, since I was a little guy and she was a taller race. So I joked about making the tallest character I could, which I believed at the time to be a female Roegadyn.
We quit playing for a while and then returned to the game a few years later.
When we came back, I decided it was time for a change and used an item that lets you change your appearance permanently. I ended up finding an old saved appearance from when I was joking about Fem Roegadyn, and just went with it.
The name Cocozan was no longer appropriate, given the lore, but I found out I could drop the Zan and it would fit fine.
So I became Coco.
It was absolutely amazing being called Coco and she/her by folks online. It wasn't the only thing that did it, but the whole thing absolutely helped crack my very thick egg.
I ended up stealing my character's name IRL, and now I have a very nerdy origin story.