Mine is butchered & shortened version of 'Sæfinn':
https://www.nordicnames.de/wiki/S%C3%A6finnIn short, when I was at University, I started writing a novel, which I ended up completing a first draft for with NaNoWriMo. Some of the characters were of a Nordic background and I named one of them 'Sæfinn' after looking up names and I found I liked it and it had some relevent meaning because IIRC it is a combination of "Sea" and "Wayfarer". Dude owned a ship. I was really into Norse stuff at the time.
Though I never did finished redrafting, I kind of hated what I wrote because I kinda crammed a lot to meet NaNoWriMo goals. In one of those days I remembe writing 10,000 words and it was probably 10,000 words of crap. But I was behind schedule and needed to catch up.
And then when creating a character in an MMORPG, I needed a name and rather than faff about, I just took one from one of my characters. Then as I ended up playing the game a lot, it ended up becoming an online identity and has stuck since. And people sometimes just shorten it to "Sae".
I used to go by the name "Seppuku" online when I was a teenager, but since figured that naming myself after ritual suicide is probably not appropriate for all online communities, so 'Saefinn' replaced it. But I guess I was a little edgy as a teenager.