If there’s really no connection, then find a different name. Like “Ultimate Fantasy Blue” or “Last Fantasy Blue”, or just change the word order and call it “Final Blue Fantasy” if you’re set on calling it final. But I’m almost certain that “Ultimate Fantasy” has been used before, multiple times, so maybe not that.
If there is a connection, then it’s a fan game. There are lots of fan games on itch, but they get taken down when the rights holder complains. Your decision if it’s worth the risk to you.