With such a heavy season eight spotlight on Brienne and Jaime, you may have forgotten about the quieter romance between Grey Worm and Missandei. Their love story begins in the fourth season when Missandei agrees to teach the commander of the Unsullied the common tongue and grows stronger in season five when an attack by the Sons of the Harpy nearly leaves Grey Worm for dead.
By the seventh season, Grey Worm confesses his love for Missandei and the pair consummate their relationship in the morning hours before the Casterly Rock invasion. Then on the eve of the Great War, the couple fantasize about running away together to the beaches of Missandei's homeland in Naath, an island in the Summer Sea off the coast of Sothoryos.
Sadly, this last event never happens because the Mountain beheads Missandei in a show of Cersei's strength as the sitting queen. Grey Worm is present at the execution and displays anguish at the loss, a rare bit of public emotion from the usually stoic commander. We can't imagine the series wouldn't spend five seasons building a relationship if they weren't going to have Grey Worm seek retribution for his lost love.
Trained in the arts of spear and shield as well as short swords for close quarters combat, Grey Worm has the tactical training and the discipline to thwart the Mountain, and he's probably the last person anyone in King's Landing would expect to break rank and go rogue.