In Godzilla: King of the Monsters, Rodan fought on Ghidorah's side and opposed Godzilla and Mothra - why? Traditionally, Rodan is portrayed as one of Godzilla's most reliable allies, but the MonsterVerse has so far sidestepped this relationship. Rodan doesn't even get to meet Godzilla until the movie's final scene, when all four Titans battle each other in Boston.
In Godzilla: King of the Monsters, the winged Titan emerges from his volcano after being awakened by the movie's villains. Shortly afterward, Rodan finds himself in conflict with King Ghidorah. The two engage in a fierce but brief struggle, with Ghidorah emerging victorious. After the fight, Rodan is seen with Ghidorah, who he has now accepted as the King of the Monsters - contrary to the Orca's call. Later, Rodan helps his new master by stopping the third M.U.T.O., bows down to Godzilla, who has replaced "The False King" as the alpha of the Titans.
So why did the movie decide to team Rodan with Ghidorah? Godzilla: King of the Monsters director Mike Dougherty explained during a watch party that having Mothra shamed Godzilla and Rodan into helping her drive off Ghidorah.
Rodan also fought alongside Godzilla in Invasion of Astro-Monster, Godzilla: Final Wars, when he was mind-controlled by aliens.
It was disappointing that their relationship from the classic Toho movies wasn't adapted for Rodan's MonsterVerse debut. It certainly would have been fun to see Rodan swoop in and dive-bomb Ghidorah again, but at the same time, it's true that Rodan fighting Ghidorah would have tipped the scales too much in Godzilla's favor, making the film's final showdown grossly unfair. With Ghidorah being left at a severe disadvantage, the fight would have been understandably less exciting.
As much as fans would love to have seen Godzilla and Rodan fight on the same side, it was simply not to be. But, that doesn't mean it won't happen. Unlike Ghidorah and Mothra, Rodan survived the movie. The film's ending set up a future team-up between the two. That means that if Rodan were to return for Godzilla vs Kong - or some other MonsterVerse film - he could finally work with Godzilla to defeat the enemy.
