Actually this was pretty easy but finding a video was killer! But The person who is Xio's Japanese voice is an accomplished actor which is Mamoru Miyano. I had Zero Kiryu from Vampire Knight as my example but the video got deleted but he also does the voices of Light Yamgami from Death Note and Tamaki from Ouran High School Host Club. Haha if you just ignore the character you actually can see that his dark voice can fit for Xio and his voice is so alluring! xD Watch the movie to the ending you see the evil part! Xio's fake side as Tamaki and Xio's true self as Light.
His singing voice, duh this guy can sing too so it's a no brainer that Mamoru Miyano keeps the singing voice for Xio as well! Of course I pick the Ouran song!!! xD