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 [[BreakOutVillain 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, whose 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

* AdultFear: A giant, city destroying monster specifically targets your children for consumption!
* AntiHero: Belvera upgrades to this here.
* ChildHater: King Ghidorah not only hates them but wants to eat them!
* CurbStompBattle: Mothra's first fight with King Ghidorah ends in a crushing defeat for the former. [[spoiler:It's the other way around once Leo is all powered up at the end]].
* TheDreaded: 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 RedBaron is the "King of Terror".
* EvenEvilHasLovedOnes: Belvera does actually care about her sisters.
* ForTheEvulz: 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.
* HeartIsAnAwesomePower: Moll tells the protagonist of the story that his sensitivity is not a bad thing.
* KnightOfCerebus: 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 the life force of 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.
* NewPowersAsThePlotDemands:
** Apparently Aqua Mothra can go back in time.
** Fairy now has a [[Franchise/StarTrek Tricorder]] setting.
* RedBaron: King Ghidorah is known as the [[NamesToRunAwayFromReallyFast King of Terror]].
* SanDimasTime: 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.
* TimeTravel: The solution to stop King Ghidorah is to go back in time and kill him in his weaker juvenile form.
* TookALevelInBadAss: 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 MidSeasonUpgrade...except for once it felt genuinely earned.