The city of San Francisco had woken this morning to an unexpected and bizarre occurrence. The city itself was under several meters of water. Overnight, something had caused the sea level to rise and cover most of the city... Then they came. A swarm of man-sized dragonflies, the Meganula. The frenzied insects descended on the city, consuming everything in sight, stealing energy from whatever source they could find with their razor-tipped stingers. But the worse was yet to come.
The survivors watched the massive insects dive into the flood waters and a short time later, float up to the surface, dead. A wave of relief washed over them, as they believed the creatures had simply drowned or reached the end of their lifecycle... but that relief soon turned to dread as the water erupted in a massive geyser. Two red eyes glowed in the eruption, which settled to reveal the massive queen of the Meganula, Megaguirus. The primordial demon looked over her new feeding grounds, emitting a screech from her toothy maw to announce that man had just gone from the top of the food chain to the very bottom. What she didn't expect was for another screech to answer her own.
The mammoth insect turned to see the massive form of the Earth's guardian, the Black Mothra known as Battra still in its larval stage, plowing through the waves into the flooded city. It was no secret that Battra had no love for the humans, even though Mothra had managed to quell his rage towards them. He had come for one reason and one reason only. Megaguirus and her kind would ravage the Earth and wipe out everything in their path should they be allowed to propagate, something Battra could not allow. Battra came to a stop, his mandibles parting to emitting a earsplitting screech of challenge at the Meganula queen... and she accepted.
Megaguirus had staked this out as her territory, that was all there was to it, she would destroy anyone or anything that dared set foot on it without her permission. Megaguirus dove straight at Battra, screeching and speeding past him, slashing his armored exoskeleton with her claw, sending a shower of sparks flying in all directions. She turned, expecting to see blood spurting from the guardian, but she realized such a feeble blow wouldn't pierce the guardian's armor too late and received a blast of purple lightning to the chest. Battra's Prism Beams slammed the prehistoric tyrant backwards through a building, shattering it beneath her bulk. Battra quickly continued his assault, firing jagged bolts of energy from his eyes and horn into the rubble. However, Megaguirus was too quick and managed to regain flight, dodging the assault. Battra followed her with his Prism Beams as she flew across the cityscape, missing the agile kaiju and blowing up buildings in the process.
Megaguirus cackled at the foolish insect's attempts and finally flew straight up and with supersonic speeds, dove straight at Battra, slashing his neck with her clawed wings, managing to hit a weak spot in the monster's armor and draw a spray of blood. Battra screeched in surprise and fury that he'd actually had his lifeblood torn from his body. Megaguirus dove at him once again from behind, only for Battra to be waiting for her and swinging around, slamming his horn into her chest and discharging energy through it. Megaguirus screamed in agony as she was knocked backwards into the water, sending up a plume of white waves. Battra refused to allow Megaguirus to regain the advantage and dove under the waves, surging straight at Megaguirus as she attempted to surface. The guardian of the Earth slammed horn first into her chest, driving her straight through the Pyramid Building.
Megaguirus felt the wind forced out of her by the blow, but had enough time to see an opening and drove her stinger into a space between Battra's armored plates on his neck. Battra screeched in pain as he felt his energy drained, then in surprise as he discovered he could no longer fire his beams. Feeling himself fading fast, Battra realized he had one option. His entire being was engulfed in orange energy which raced skywards, out of Megaguirus' clutches. Megaguirus looked up in surprise as in an explosion of energy, Battra became his imago form.
Taking advantage of the Meganula Queen's shock, the evolved Battra unleashed concentrated beams of prism energy from his eyes, smashing Megaguirus in the chest, forcing her back. Before she back pedaled, Battra pelted her with even more energy beams, forcing her into the San Francisco Bay area. Megaguirus finally recovered from her surprise and evaded another beam meant for her. Megaguirus flapped her wings at blinding speeds, causing computers in the surrounding area to spark and short-circuit. She then flew straight at her now airborne foe with blinding speeds and bit down on one of his legs. Battra screeched in agony as blood spurt from his limb but replied by biting Megaguirus' eye. While he didn't have as strong of jaws as the primordial titan he faced, he bit a more sensitive area, drawing a torrent of blood from Megaguirus' eye as he tore into it. Megaguirus screeched in agony and had no choice but to retreat from her assault.
Battra looked down at his leg, which was now limp and useless, not to mention pouring blood. Battra ignored it and fired at Megaguirus again, only for her to dodge and be right behind him. Battra turned in time for Megaguirus to draw on the energy she'd stolen from him, forming an orb of purple and orange energy before her and letting it loose. Battra was sent plummeting from the sky by the force of the energy orb detonating on impact with his body. Battra fell hundreds of feet and crashed through a seaside building, smashing it to pieces. Megaguirus screeched in pleasure, watching her opponent lay in the rubble, seemingly defeated. She lowered her stinger and dove straight at him with the lethal weapon. Battra looked up and saw Megaguirus coming, unleashing his Prism Beams in self-defense. Thankfully, he landed a direct hit on her wing, blasting a hole through its leathery membrane. Megaguirus screeched in pain and ceased her attack so she could concentrate on keeping herself airborne with her wounded wing. Though she managed it, Battra took the time to recover and take to the sky, flying out over the bay. Megaguirus, as hurt as she was, refused to let her prey escape her and flew after him as fast as she possibly could. Battra was thankful for the lucky hit, as it slowed down the prehistoric insect enough that he could outrun her. Still, he realized that for his best chance of winning he'd need to do something quick.
Megaguirus, snarled, refusing to let herself be outrun. She flapped her wings as fast as she could manage, speeding up enough to get within melee distance of the Earth's guardian, lunging out and biting down on his wing, tearing a chunk out of the back. Battra screeched in agony as he lost some altitude over the Golden Gate Bridge. He turned and unleashed his Prism Beams on Megaguirus. The larger monster ignored the pain the searing beams of energy torn into her hide and finally reached Battra, driving her stinger into his chest, the end of it erupting out of his back in a shower of blood and gore. Battra screeched in agony, knowing he'd suffered a mortal wound but refusing to surrender. He looked up, his vision blurring as Megaguirus pulled him up with her tail so she could feed on his flesh...
As Megaguirus opened her maw to bite his face off, Battra let loose with all his remaining energy, the beams of energy going straight into her jaws. Megaguirus' eyes went wide in shock as she realized her mistake too late. The beams tore through her body, erupting out the back of her head, taking her brain with it. Megaguirus' body went limp, her eyes going black as she plummeted from the sky, Battra impaled on her tail as both plowed through the Golden Gate Bridge and into the bay.
Battra looked up as he and his foe sunk into the depths, seeing humans looking down through the hole in the bridge as blood poured up from both to the surface. Realizing he was dying but had succeeded in his mission, he allowed life to leave his body, knowing he'd be revived someday to defend the world yet again. With this thought in his mind, his eyes went black as he and Megaguirus continued to sink.