T'Challa tried to kill Steve's bestie, right? A man under Steve's protection. And now they're in Wakanda for the foreseeable future.

T'Challa's got a nation to run, but he's also got a good man with a heart of gold and balls of steel or vibranium ahahaha to make amends to - and a super soldier stamina to test out. He decides that even a king can willingly to go his knees for a man like Steve.

(NGL I've loved these two for ages and have been waiting for Civil War to prompt something like this)