[@Gareth] Basically, its a big battle royale between thousands of random individuals called 'King Candidates' from Heaven, Hell, and Earth to find a suitable ruler who can bring all three realms together. It is almost impossible for a human to be a candidate without demonic or angelic heritage, particularly those with recent heritage.
There doesn't only need to be one candidate alive at the end, as it is perfectly viable to form alliances, although said alliances must have one candidate to be the ruler, and the rest of the candidates in the alliance would be their 'court'.
Of course, that doesn't mean it won't be easier for some to just start fighting and killing every other candidate either.
Also candidates [i]might[/i] get special powers, just so the weaker humans aren't killed immediately by demonic and angelic candidates, who would already have certain abilities.