Boken no Konoki

The Hylian Dragon translated to Dhaos the Demon King

Legend of Cress
Dhaos was Sealed with Amane Nishiki's Body. Konoki Controls Amane to kill Mars Uldole and to meet Cress, Mint, Chester and Morrison.

Legend of Yuri
He was seen in the seal when Amane gets to worried about Yuri would never return home.

Legend of Yuki
Yuki was sure about relationship with Amane and was at the same relationship with Martel.

In Tales of Phantasia
Dhaos the Demon King was a Human or a Dragon released by Mars.