Siôn

I really like this name! And to clarify on pronunciation, it is pronounced "Shown", as in the phrase "the film was shown on TV". So, not "Sean", not "Shorn", not "See-on", but "Shown" (with a long "o").

The person above is incorrect. It's not pronounced "shown" It's pronounced just like Sean, Shaun, Shawn etc.
I can guarantee I'm correct, I'm Welsh and I have a cousin called Sion, and I know countless Sions and they all pronounce it just like Sean.

Met someone called this, and they pronounced it 'Sean'. I called him Sion though as I had no idea, and of course he laughed. It's such an unusual name these days!

Sion is pronounced 'SHORN', the same as the Irish Sean.