Arthur Pendragon, King of Knights, Wielder of Excalibur and a legendary hero in his own right. With the unique nature of servants and the Grand Order, he can be found in time periods not just his own. Ranging from being summoned to those places, or simply existing in the modern day as a result of Chaldea. Still, Camelot would be the most likely place to find the King. Interactions with Proto Merlin and other Servants would be great, but not necessary. With a Fate based route, the other person could easily be his Master or some other Servant's master. Otherwise a more standard Camelot/Fantasy scene would work well. While the King is known for pulling the sword from the stone... well... it's probably obvious where that reference is heading.
