.. wait. It's all well and good adding these guys to categories, but we should probably simplify/automate and organise.. whatever it is we're trying to do here.
The Stories have a field for Character which is expandable, the idea being that you can list each character which has appeared in that story.
The Characters have a field to represent what series the character belongs to, not what they've featured in.
Surely the stories field is the one you want to fill out in this instance? I'm not sure we can successfully tie the Character noted in the Story to a Series, though.
Otherwise you'll have to add each series reference to the character template for each little appearance they make, and you'll have no record of WHERE they made the appearance. If we went that route then we should probably introduce a new field, like "appeared in", where you can list series.