Anything useful/meaningful to them as long as it belongs to them and not another character is fine! It doesn't have to be on them at their current canon point.

I think that should be fine! For the sake of the game, we can just say they're a butterfly spirit or a sylph (air spirit) in butterfly form for some minor powers if you would like. We're aiming to be lenient as long as it's in the ballpark so that people are able to be creative, especially as there is a lot of variation in various myth interpretations throughout the world. So you can say it's without powers like canon if you want to go for meaningful, or you can give it air/wind-related abilities and say it's a sylph. Whichever works for you!