I do not feel that playing such a character would be much fun myself. Others may though. I just keep trying to figure out what one would do as a Capetian. Follow the Noble/Unit. Be automatically included in battles if I am in the same region of my Noble/Unit when a battle starts. Get the same feedback a Hero gets and the same risks. Possibly pay the unit. Role play. I really do not see anything that this character would be actively DOING aside from following the Noble/unit around and paying the men.
Adventurers hunt undead, repair equipment, move around, collect bounties etc...
Priests preach, hold lordships, act as ambassadors etc...
Nobles lead units, rule regions, lead armies, rule countries, serve as diplomats, etc...
Captains follow nobles around...
I do think, however, that this would make a great system for NPC Captains... Another thread!
