Challenge day in the Comics is basically a royal rumble. Seems anyone can challenge on that day.
Then their are also tribal challenges, which are direct challenges to the Black Panther in a 1v1 fight. Very inconsistent who can do this but so far it really seems like "anyone." We've seen outsiders like Mbaku and Killmonger famously challenge but we've also seen some random dude named G challenge Shuri. The BP just has to accept.
http://blackpanthermarvel.blogspot.com/2016/12/panther-powers-part-3-annual-tournament.htmlMovie is royal blood (hence Shuri jokingly saying she would challenge and of course Killmonger) or a representative from one of the tribes can challenge.
What is interesting in the movie and not 100% clear is what happens when the King ages out of the Black Panther role. The Challenge Day scenario seems to be only a coronation for the King. It is only to become King. So it only happens when the King gives up the throne.
But we obviously know T'challa was Black Panther toward the end of T'chaka's rule before T'chaka's death. And we saw on challenge day that not all the leaders of the tribes were the ones fighting. The River tribes leader was the Lip Plate dude... yet Nakia was the warrior for example. However, M'baku was both the warrior and the leader of the Jabari.
So if say... Nakia faught and beat T'challa... is Lip Plate dude the king? While Nakia is black panther? That is unclear.
And how does the king choose the next black panther when he ages out? Is there a separate tournament? Is it just his choice? It would be cool if there was a separate thing similar to the rite of ascension or something.
One of my little issues with Black Panther, the comics more than the films, is that it hasn't spent much time exploring how its government works
Agreed. Unfortunately, you would need a true comic writer who wanted to keep things unique and fantasy like about Wakanda to do it. Like Kirby who invented challenge day, Don who added fantasy elements to the HSH ceremony, Gillis who added various tests to the king, and Priest who added political stuff like the Doras and such.
But... when it ends up being someone like Coates, all you get is, "lol this is so stupid lets make it like real life" where the King just says he sucks over and over and institutes a consitituional monarch... why functions the same as the tribal council and they move on, making the whoel first arc a big waste of time and only serving to ground something that doesn't need grounded.
I would love for a comic guy like Ewing, who loves his deep canon connections, to re-vamp and explore the Wakandan government. Or someone with a big Sci-Fi love like Geoffrey Thorne do it. I just can't be a dude who wants to make it real life.