The final film in the Rebirth of Mothra trilogy, this movie is considered the strongest entry. The environmental message has been toned down, the monster battles have improved, probably helped by the return of King Ghidorah. The child protagonist is thoughtful and reserved, which many see as an improvement over his more vocal, childish predecessors. He and some of the Elias sisters go through character development, and actual tension is present.
Belvera has infiltrated Infant Island, tricking Moll and Lora into reviving the powers of the Elias Triangle. After a brief scuffle, she escapes, warning them of the approach of the King of Terror. A meteor lands in the forest of Fujiyoshida City, witnessed by the family of a troubled boy who dropped out of school. The boy, Shota Sonoda, goes to his favorite hiding spot in the forest. King Ghidorah has risen, spiriting children off to a dome in Aoki Forest and reigning destruction upon areas of Japan. There is a great aerial battle, but Mothra Leo is no match for King Ghidorah and Lora gets brainwashed in the process. Moll, Fairy, and Shota meet up and go to Leo, where he learns the children will become King Ghidorah's meal. Leo determine that the only way to stop the monster is to go back in time, and Moll sacrifices herself in the process. Her dying wish is for Shouta to save Lora, who’s in the dome. While Mothra Leo squares off against the young but strong Cretacious Ghidorah, Shota must save Lora before they and all the children are eaten by Ghidorah...
Tropes used in the films include:
- Anti-Hero: Belvera upgrades to this here.
- Child Hater: King Ghidorah not only hates them but wants to eat them!
- Curb-Stomp Battle: Mothra's first fight with King Ghidorah ends in a crushing defeat for the former. It's the other way around once Leo is all powered up at the end.
- The Dreaded: There's a reason that Belvera has no delusions of controlling King Ghidorah like the previous villains and her sisters take his return extremely seriously. There's a reason Ghidorah's Red Baron is the "King of Terror".
- Even Evil Has Loved Ones: Belvera does actually care about her sisters.
- For the Evulz: King Ghidorah is able to obtain his stockpile of children to eat by just teleporting them all to his dome to prepare for consumption, without needing to destroy anything. He then proceeds to occupy his time waiting for his meal to be ready with wanton destruction anyway just for fun.
- Heart Is an Awesome Power: Moll tells the protagonist of the story that his sensitivity is not a bad thing.
- Knight of Cerebus: King Ghidorah. While the previous two main monsters were no push overs, the moment King Ghidorah arrives on the scene, the movie takes a much darker turn than the previous films, with him being the first kaiju Belvera has no delusions of thinking she can control. He then proceeds to abduct every child in Japan to slowly devour their life force while he destroys everything in his path. He's so powerful that Mothra stands no chance of beating him in the present and can only go back in time to try and kill his weaker, younger self.
- New Powers as the Plot Demands:
- Apparently Aqua Mothra can go back in time. However, this was enabled by Moll's magic rather than an inherent ability.
- Fairy now has a Tricorder setting.
- Red Baron: King Ghidorah is known as the King of Terror.
- Retcon: The first movie states that Desghidorah killed the dinosaurs. This film adds that Cretaceous King Ghidorah was involved in an earlier mass-extinction event, 130,000,000 years ago (as opposed to Desghidorah's arrival 65,000,000 years ago).
- San Dimas Time: When Mothra goes back in time to kill the young Grand King Ghidorah when he was weakened, the present continues moving on with King Ghidorah only starts feeling the effects when Mothra Lea harms himself in the past.
- The Slow Path: Leo cocoons himself for millions of years to return to the present, becoming Armor Mothra in the process.
- Time Travel: The solution to stop King Ghidorah is to go back in time and kill him in his weaker juvenile form.
- Took a Level in Badass: Mothra in this film. For once Leo has to handle Ghidorah, at least he in his youth, all by himself and pulls a heroic sacrifice to stop him. It was nearly all for naught, a piece of Cretaceous Ghidorah remained in the past to regenerate and return in the present, only for Leo to get his usual Mid-Season Upgrade... except for once it felt genuinely earned.
- Would Hurt a Child: A giant, city destroying monster specifically targets your children for consumption!