I feel like this wouldn't work well, due to reasons a lot of people are already mentioning. FBTN with a large character in territory would be incredibly strong, and some characters just shouldn't be given CBN. Also, your ignore gets broken by any "Cannot be Ignored" effect, though that is the least of the worries. Set-aside would accomplish that part better.
I feel like this would make for a better fortress, where the 'leader' would sit. This would also allow you to avoid making a new term, since you could have the identifier clarify that it "holds one x, y, or z" instead. Next, you don't have to worry about the character going in battle as long as you use a "while occupied" condition. Finally, you have an ongoing condition from the fortress as normal for the card type. As long as the ability were worked out, this could be made into an interesting fortress.
One last thought, this should only hold and affect humans, IMO.