I'm leaning towards Kasai (Forest Fire) as a name, I can picture some small child having named him that way and not noticing the implications. Who thought it would be a good idea to have a forest themed village in the Land of Fire, anyways? >.>
The MC definitely think himself as such to his great angst, but he needed a name from the time he was just some kid in an orphanage. Not even the most spiteful of villager would dare just call him 'kyuubi' with the way the law of secrecy over that particular fact operated.
I knoooooooow but wouldn't it have been a bit mean towards the gm to throw a sudden curveball like that? God the faces on everyone's... faces. Would have been hilarious!