Leo differs from Mothra as he is commonly labelled as a male. Plus, unlike Mothra who is usually portrayed as being concerned more for the plights of her homeland and people, Leo takes on a more active role as a protector of the Earth, as well as taking on a Gamera-like affection for children.
In the Rebirth of Mothra universe, Leo and Mothra were the last remaining members of a highly advanced species of giant moths created as guardians to the Elias, an ancient civilization of small yet powerful humanoids far older than humanity.
Leo first appeared as an egg laid by an aged and weakened Mothra in 1996. He hatched prematurely during a battle between his mother and a monster called Desghidorah and, despite being hopelessly outmatched in his larval form, attacked his mother's aggressor. After a long battle, the two managed to escape, though by that point, Mothra had been badly wounded, and she collapsed into the sea. Despite his best attempts to help her, Leo could do nothing as he watched his mother sink into the depths. Leo then retreated to a remote island where he cocooned himself against a 10,000 year old tree. After some time, Leo emerged as a swarm of multicolored butterflies which merged into one giant insect. Leo then flew to Hokkaido to do battle with Desghidorah, and arrived in a flurry of laser and energy beams. The demonic dragon could not stand against the power of the new Mothra and was soon defeated. With the help of the Seal of Elias, Leo imprisoned the beast once again within its ancient tomb. Leo then went on to replenish the land destroyed by Desghidorah, releasing a powder that sped up the growth of Hokkaido's flora. With the forests and fields returned to their original beauty, Leo returned to Infant island.
Mothra Leo was called upon again when an ancient pollution-eating monster called Dagahra began infesting the ocean with toxic parasites called Barems. Leo attacked Dagahra and seemed to have the upper hand, until the battle was taken underwater. Unable to combat Dagahra in his element, Leo was overwhelmed by a swarm of Barem and awaited his opponents' killing blow. However, with the assistance of the Elias, Mothra Leo was replenished by the water spirit Ghogo and was transformed into a new form, Rainbow Mothra (レインボーモスラ?, Reinbō Mosura). Suffused with the water spirit's ancient magic, Rainbow Mothra re-entered the fray, relentlessly assaulting Dagahra. Yet, when the toxic one retreated below the waves, Rainbow Mothra followed suit and dove under the water, transforming himself into his new aqua form, Aqua Mothra (アクアモスラ?, Akua Mosura), and finishing off Dagahra. With his foe defeated, Rainbow Mothra then flew off into the horizon and thus, the world is once again safe.
Rainbow Mothra was awakened again to fight King Ghidorah when he was eating humans. The two fought, but Rainbow Mothra was quickly defeated. Rainbow Mothra was transformed into Light Speed Mothra (光速モスラ?, Kōsoku Mosura) and went back in time to kill King Ghidorah when he was weaker. He went back to the Cretaceous period, where he fought Cretaceous King Ghidorah. He defeated Cretaceous Ghidorah, but his tail was buried in the ground. Cretaceous Ghidorah regrew from the tail, and arrived in the present only a day later. Leo attacked King Ghidorah as Armor Mothra (鎧モスラ?, Yoroi Mosura), and killed him. Armor Mothra transformed into Eternal Mothra (エターナルモスラ?, Etānaru Mosura) and flew away in peace.