Avengers 4: 10 Things Fans Demand
4. Nebula Lands The Killing Blow
One of Infinity War's crowning successes has to be the way it handled the relationship between Thanos, Gamora and Nebula, and with the Mad Tyrant's favourite child now dead, it falls to Nebula to finally get her revenge.
In the comics, Thanos' least favourite daughter actually succeeds in claiming the Infinity Gauntlet for herself, before embarking on her own kind of tyranny shortly thereafter. That's not likely to happen here however, with Karen Gillan's version of the character being decidedly more heroic now than when she first started.
Throw in the little matter of a dead sister to avenge, and you have all the thematics in place to make Nebula the one who kills Thanos for good. There are obviously more popular characters who could be optioned to perform that particular task, but there's only one way (feasibly) that Thanos leaves the mortal coil for good - with Nebula delivering the killing blow.