A hidden detail in Godzilla: King of the Monsters makes Rodan a traitor to Godzilla in the MonsterVerse. In the movie, Rodan fought as a minion of King Ghidorah after losing to him in Mexico. Rodan remained on Ghidorah’s side until the end of the movie, when Monster Zero was finally slain by Godzilla.
Traditionally, Rodan is depicted as an ally to Godzilla, and not the villains. In 1964’s Ghidorah, the Three-Headed Monster, Rodan famously teamed up with Godzilla at the behest of Mothra to save the Earth from Ghidorah. The two returned as a duo to beat the villain one more time in the direct sequel, Invasion of Astro Monster. In Destroy All Monsters, Rodan was one of the kaiju was contributed to Godzilla’s third victory over Ghidorah. After Toho rebooted the franchise in the late 1980s, Rodan sacrificed himself to help Godzilla beat Mechagodzilla in 1993’s Godzilla vs. Mechagodzilla II. His MonsterVerse counterpart, on the other hand, was denied an opportunity for a team-up in his only movie appearance thus far.
While it’s true that Rodan didn’t get to meet Godzilla until Godzilla: King of the Monsters’ ending, a hard-to-spot detail in the movie’s underwater city sequence indicated that the two did know each other in the past. One of the drawings on the walls showed Godzilla, Mothra, and Rodan all on one side, fighting Ghidorah. This suggests that thousands of years ago, Rodan was originally on Godzilla’s side in his battle with Ghidorah. This reveal means that the MonsterVerse’s Rodan essentially betrayed Godzilla when he joined forces with Ghidorah. It would seem that in the distant past, Rodan was actually Godzilla’s ally, yet he still teamed up with his ancient rival in the modern era.
The implication provided by the movie’s story was that Rodan had no prior relationship with either Titan, but the Easter eggs in Godzilla’s underwater lair paint a better picture of the Titans’ history. Rodan is apparently a traitor who has now switched sides not once, but twice. That puts him in contrast to Mothra, who has been in Godzilla’s corner every time, including the ancient fight with Ghidorah, their modern-day battle, and presumably, the original Titan War with Kong.
For Godzilla, Rodan’s lack of loyalty may be a warning sign for the future. Godzilla didn’t summon his Titan minions from Godzilla: King of the Monsters for the fight with Kong in Godzilla vs. Kong, but could end up needing them in later MonsterVerse installments, especially if he ever has to fight multiple villains. Due to their history together in Toho’s films, Rodan would be a favorite choice for such a role, but what’s known about his past doesn’t exactly make him trustworthy. If Rodan is ever put in a situation where he thinks the villain is in a better position to win, Godzilla may have to watch his back. There’s unfortunately no guarantee that Rodan will fight beside him until the very end.