Twenty-three years ago, somewhere outside Terra's solar system, a star collapses into a black hole. At the same time, a cluster of Godzilla Senior's cells encased in crystal drifts through space. The cells absorb the great energy emitted by the collapsing star and start dividing. As a body is formed, it incorporates the crystals into its structure. Xenilla is born. As soon as he gains sentience, he is bombarded by visions of his home world Terra. Of a silhouetted monster burning it to ashes. Enraged, he declares he will stop it. After quickly mastering his abilities, such as telekinesis to travel through space, he begins his journey home. It takes him several years to reach it, but he doesn't care as long as he defeats this destroyer and claims his territory, no matter what it takes. He finally reaches the asteroid field and battles M.O.G.U.E.R.A.
Twenty-three years ago, somewhere in Equestria's Hollow Shades forest, an Earth Pony mare named Melody Chime waits out the rain in her log cabin while strumming her guitar. There is a knock at the door, and she calls her husband Lead Choir, concerned about somepony disturbing them at this late hour. They open the door to find a Diamond Dog panting in exhaustion carrying something wrapped in a blanket. The figure reveals he's carrying a newborn Pegasus with pink fur and a mane composed of cream, magenta, and purple stripes. The Diamond Dog explains that the child's mother was a good friend of his, but the child's parents are dead. He has little time to explain and must leave soon, but the child must be cared for. The couple assure him the child will be cared for. He gives his thanks and one last goodbye to the foal before running off, and Lead Choir watches him leave until he suddenly vanishes into thin air. Surprised by this turn of events, Melody examines the blanket and marvels at how it is as soft as silk, yet catches the light and shines like crystals. Melody decides to name their new baby girl after their wedding song: Mi Amore Cadenza.
Xenilla and Blade Dancer find Key Ring and ask him to examine the black crystal they found the other day. When Xenilla opens the casing he put it in, they feel the room grow cold and just looking at it feels wrong. Key Ring explains it is an Aerenth crystal. Aerenth is banned because it can only be created using dark magic.
Xenilla asks him to define dark magic, so Key Ring explains how regular magic is fueled by positive emotions like joy and hope, but dark magic is fueled by negative emotions like greed, rage, and hatred. Practicing dark magic is banned because only a select few are disciplined enough to use it without being consumed by the negative emotions, and besides, it has little use besides hurting others.
To be on the safe side, Xenilla makes another container for the Aerenth, and he and Blade Dancer describe how they found a large patch of Aerenth. Key Ring becomes scared and says he only knows of two individuals powerful enough to make such a large patch. He uses a projector to show some slides. The first is Nightmare Moon, but it cannot be her because she was a corrupted Princess Luna and was purified by the Elements of Harmony. The second is King Sombra, but it also cannot be because Spike and Princess Cadance killed him with the Crystal Heart. Xenilla recalls where the patch was located and suspects Sombra is not as dead as they think. Little do they know that Sombra is on the roof of their building.
Princess Cadance wakes up and groans. Lately, she's been plagued by nausea and fatigue, disrupting her sleep cycle. She finds a note from her husband Shining Armor telling her to rest and relax as he will handle the affairs of state for the day. She smiles and decides to let the citizens tour the ewe stables.
King Sombra observes Xenilla and the others with pure hate, and stomps on the roof so hard it cracks. Declaring that a pony with power rivaling his cannot be allowed to exist, he fires a blast of dark magic at the roof. Down below, Xenilla considers his options. He is sure Sombra is here and trying to assassinate Cadance, and he debates with himself whether it would benefit him to interfere or not. Suddenly, the ceiling collapses. Blade Dancer knocks Key Ring out of the way of falling debris, but is almost crushed herself until Xenilla catches the debris with a combination of his brute strength and telekinesis.
Key Ring finds Aerenth embedded in the debris. Xenilla extends his senses through the crystals and detects Sombra moving away from them. Angered that he would try to kill them and then run away, he levitates himself to the roof and pursues, telling the other two to tend to any injured and warn the princess. Blade Dancer catches a glimpse of Sombra.
Cadance and Shining Armor are mingling with the citizens in the ewe stables when they hear an explosion. Xenilla pursues Sombra across rooftops, firing his Corona Ray and throwing crystal lances, missing several times. Not seeing Sombra and thinking Xenilla is up to no good, the royal couple order Flash Sentry to assemble the guards while they deal with him. Xenilla fires a shot that knocks Sombra off a roof and into an alley, but before he can follow him, Shining Armor traps Xenilla in a forcefield bubble, and Sombra slips away. Xenilla pounds away at the forcefield and makes it crack a little, while Cadance yells at him for violating Sacred Hospitality and attacking her citizens, as his missed attacks damaged several buildings. Blade Dancer and Key Ring arrive and try to explain that somepony tried to kill them and Xenilla was chasing him, but Cadance is in no mood to listen. Flash Sentry reports there were several injured but thankfully no fatalities. She declares that Xenilla will be imprisoned until evidence can be found that what they say is true. Blade Dancer and Key Ring want to present the Aerenth, but they can't find it in the wreckage. As Xenilla is dragged to prison, Blade Dancer shares with Key Ring that she is sure Xenilla is getting arrested on purpose, since he is strong enough to easily escape if he wanted to. Shining Armor notices how stressed Cadance is and tells her to rest.
The prison is under the castle. Blade Dancer enters to find Xenilla is the only prisoner. He snaps his chains and explains that he is exactly where he wants to be. Sombra wanted to wait until he was incapacitated until he made his move on Cadance, but since he can sense Sombra's presence, he'll be able to intercept him. There's just one problem he didn't foresee. The cell door will trigger an alarm if it is broken down, and if that happens, they will lose the element of surprise. She offers to help him escape if he promises to do his best to save Cadance, and he agrees.
The warden Lockdown and his second in command Dusk Shift walk in and ask what is going on. She bluffs that Shining Armor ordered Xenilla to be brought to Cadance's chambers for interrogation, but Lockdown points out the royals would have told him personally if that were the case. Left with no other choice, Blade Dancer attacks them. She gets slashed across the cheek, but manages to knock them out, then takes their keys and unlocks the cell. Xenilla creates a crystal with his powers, crushes it to powder, and applies it to her wound to instantly heal it, amazing her. Suddenly, he shoves her into the cell and locks it, saying this battle might get ugly and she'll be safe in there, and he'll free her when it is over. He walks out with her yelling and complaining about typical male chauvinism.
Sombra uses his shadow form to enter Cadance's chambers to find her sleeping. He creates Aerenth constructs to shackle her limbs and readies an Aerenth spear. He muses that he always wanted to rape an Alicorn, but he'll settle for the satisfaction of killing her. She wakes up and frantically struggles, managing to crack her bonds a little. He gloats that even with her Alicorn strength she cannot save herself, but before he can plunge the spear into her heart, Xenilla bursts through the door and tackles him, sending them both through the window.
The two crash through the roof of the main hall. Sombra is enraged and says he has interfered with his plans for the last time. They battle, with Sombra's Aerenth constructs, dark magic blasts, and brute strength vs Xenilla's crystal constructs, Corona Ray, and brute strength.
Cadance finally manages to break through her bonds. She has no idea how Sombra is back and why Xenilla saved her, but she is a princess, and her first duty is to protect her people. She opens an ancient cabinet and looks upon the suit of armor inside.
