Perhaps Gray could take on the role in an alternate storyline. Gray has always had a sense of justice, and his cool - headed nature could be developed into that of a 'Prince of Peace'. He could learn a new form of ice magic that has the ability to freeze aggression and hatred, thus bringing peace to the areas affected by conflict. For example, when dark guilds start causing trouble, Gray uses his new powers to stop them without having to fight in a violent way.
One common theme could be redemption. The prince of peace might be on a journey to redeem himself or others. Another could be love, perhaps his love for his people or a romantic love.
The main theme is likely peace. Since it's about the Prince of Peace, it will probably focus on how peace is brought into the world through the Christmas story.
Well, it could be about a prince who brings peace in a land full of chaos and then there's a lemon element, perhaps a lemon tree in the prince's garden that has some magical or symbolic significance. Maybe the prince uses lemons to heal the sick or as a sign of hope during difficult times.