Grey is a bit of a hesitant guy due to having amnesia, but he shows a lot of determination to get to the bottom of who he used to be and to help his newfound friends save their home. He should sound like the usual teen-hero protagonist in a way, but not overly cocky. Try to sound more down-to-earth and perhaps even tired - the poor guy just woke up an hour before fighting off a giant evil murder swan, after all. I'm down to hear anything you'd think would fit this, just try not to sound too deep. A good example of a base voice to try putting your own spin on would be Revali, from the Legend of Zelda.

At later points in the story, you should be able to show more emotion as Grey matures emotionally and becomes more invested in the fate of the kingdom. There will be angry and emotional lines, possibly tears.