In the comics, K'un-Lun is one of the Seven Capital Cities of Heaven, and each has an Immortal Weapon, Iron Fist being K'un-Lun, and once a century or so they all merge into one for a tournament between the Immortal Weapons.
So in Rivals, the timestream entanglement has prematurely set off the convergence and Doom's usual usurping attempts in challenging Shou-Lao for the power of K'un-Lun has prompted a new contest, but all the Immortal Weapons but Iron Fist are MIA in the timestream, so we get others chosen from the heroes present to represent the other cities, and apparently the Eighth City too judging by Daredevil (in the comics the Eighth City was fallen and turned into a giant prison for demons, here in Rivals it's been turned into a sanctuary that Daredevil is serving as leader of). And Doom is apparently backing a challenger too.
