Chibi Moon swears, frantically digging through her belongings in her dormitory room while stressing over something due in an hour and a half. Eventually, she finds an archaic wooden lockbox with a lunar symbol on it, a hand-me-down from her mother she isn't supposed to open until her sixteenth birthday. However she decides desperate times call for desperate measures and after finagling with the locking mechanism, she gets it to react to her magic after falling over and getting conked on the head. The locks reconfigure with the emblem on the front shifting from a crescent moon to a full moon, popping open. Inside is a collection of increasingly old envelopes and scrolls from Neighpon. It's revealed there is a legacy of beings called Senshi in Neighpon going back hundreds of years. Many of the old letters and scrolls of memoirs of past Lunar Senshi who passed on their lessons to their successors alongside having pictures and paintings of their respective team, mostly comprised of kirins but Neighponese ponies and occasionally other species like a gryphon or mermare are present. Chibi is evidently next in line to inherent the Lunar Senshi position with her mother being the current one. Chibi eagerly goes through the records, thinking centuries worth of memories by those who fought of evil would surely give her something she was looking for.
Much to Chibi's chagrin however, a vast majority of the memoirs are just morality lessons she skimmed over. Exasperated, she groans in frustration and is about to give up, thinking it was hopeless when she notices a small sack. Left behind by the 28th Lunar Senshi, Mei Hino, the sack contains a magic charged powder based on Mistmane's design and a damaged tag that says it helps to bring understanding between parties. Much to Chibi Moon's confusion and fright, she finds the back of the tag has what seems to be an expiration date very soon. Electing it's better than nothing and might just be the ticket she needed, she hops up and rushes out of the room only to run right into her sensei, Godzilla Junior. Having come to walk her to school on his day off, Junior agrees to accompany her elsewhere as well when she nervously asks for moral support; but he isn't told what's going on.
Chibi spends an hour training her magic while Junior watches confused. As they walk through the halls, he tries to ask what is wrong, but she just keeps saying she needs moral support. Suddenly, he sniffs something and tries to find some place to hide. She levitates up to him and says he can't leave because she needs him, but he says he has to hide or else he will be in big trouble. She grabs his face and creates magical walls to push against. He is strong enough to break through them, but does it carefully so she doesn't get hurt. They start yelling at each other in Japanese/Neighponese. The powder in her saddlebags starts glowing, then flashes over them.
Two mares round the corner. One has lime green fur and a teal mane and one has orange fur and a white mane. They are lovely, looking to be an age in between Twilight Sparkle and Princess Cadance, but strangely, their manes look like they are wet even though it is has been a dry day. They almost bump into Chibi and apologize, calling her "Miss", and walk off, muttering they were looking for somepony. Chibi gets confused that they called her "Miss", then is shocked to find everything seems smaller. Then she realizes she is the one who is bigger. She sees her reflection in a mirror and finds she has become an adult. She turns around to find a disoriented Junior has become a chubby colt with light green fur and a tanned yellow-green mane arranged in a curly set of clusters that resembled a rounder version of Godzilla Junior's spiky mane. They have swapped ages: Junior is now eleven and Chibi is now twenty-five.
The two freak out and she accidentally steps on his tail, causing him to involuntarily fire a small Atomic Breath through an open window, but the heat still activates the fire sprinklers. The school evacuates and fire fighters come, but finding no fire, they leave and the students and teachers reenter the building. Junior again hides from the two mares until they walk away. Chibi asks why he keeps hiding from them, and he says he recognizes them as Nixie and Ondina from Mako Island. He can recognize them despite their pony forms because they smell like fish. She slaps him and says that was rude. Anyway, he starts yelling at her for changing them and orders her to change them back. Bystanders are confused by the sight of a child scolding a grownup, but they can't understand them because they are talking in their native language.
Chibi checks her saddlebags and finds the powder has been used up. Junior again asks what this was all about. She explains that she found out she was on a list of students to be sent to the dean. She believes because she scared so many during her entrance exam with her destructive power, this means she will be expelled. He softens and asks if she is really sure that is true. She says there were fifteen on the list and fifteen students about to take the entrance exam today, so she is sure they are going to be replaced. She wanted to retake the exam now that Junior taught her how to control her powers so she can prove she belongs. The magic powder was supposed to encourage understanding, and she was planning to use it on the judges. But the powder did this instead and now she is doomed. He nudges her and says not to give up hope.
She then brings up another problem. Her mother's Moon Senshi powers were supposed to flow gradually into her as she grew up until her mother was ready to retire. Now she is an adult, and there can't be two of the same kind of Senshi at a time. He tells her to calm down. He may not know much about magic, but Mothra Lea taught him that any spell can be undone. The problem is she doesn't know how the powder works. He says they should do research and starts to walk to the library, but she stops him. Her hair springs up slightly and the crescent moon on her Cutie Mark becomes fuller. Her voice becomes more assertive, but she bewilders him by talking melodramatically and calling them Legendary Warrior Monster King Godzilla Gojo the Junior and Lunar Senshi Successor and Kaiju-Trainee Chibi Moon. She claims it is how the heroes in her manga talk. Anyway, they need to take care of something before they can move freely through the school.
They go to the attendance office. Chibi, claiming her name is Black Moon, says she wants her nephew to enter the school. The clerk mistakes Junior's confusion and awkwardness for shyness and asks for his name. Chibi quickly makes up the name Minya, which slightly offends Junior but he manages not to blow their cover. The clerk looks at her notes and says normally, parents or guardians let the school know ahead of time. Chibi claims that she wrote a letter, but in traveling all the way from Neighpon, they most likely beat it to the school. The clerk finds this plausible. Equestria knows of an expedition of ponies that settled into Neighpon and intermarried with the local Kirin population. Chibi and Junior both have features that would indicate Kirin ancestry like a slightly crooked horn. The clerk says he should fit in, as he already knows how to speak Equestrian, and even better than that filly Chibi does, offending her. She just has to fill out a form and "Minya" will take the entrance exam in the afternoon. However, since this is so last minute, he'll have to take a pre-exam to prove worthy of the entrance exam.
They leave the office and Junior asks her what was she thinking, as he can barely cast any magic, even levitation. She again talks melodramatically and he tells her to stop it. Suddenly, she sparks with power and the moon on her Cutie Mark becomes one third full. She starts crying and says she can't stop it. He softens and says he is trusting her to fix this, but if she can't, they must find one of the princesses. She begs him not to do that. He says they should fix this before anypony notices he is missing. The last time he went missing, Princess Luna went berserk and stormed Mako Island. Chibi is sure she can reverse the powder's effects if she can learn about it.
She tells him to pass the pre-exam and fail the entrance exam, so that there will be one last student to replace the ones on her list. The pre-exam is just basic reading, writing, and history. He points out if he can't demonstrate any magic during the entrance exam, the judges will get suspicious or ask him to come back later. She tells him to just use his Atomic Breath. It doesn't matter that it is not really magic, because they don't know that. He then points out that on the off chance he is accepted, then if "Minya" disappears it will be really suspicious. She says it is highly unlikely he would be accepted, as the judges don't like destructive, non-standardized magic and only accepted her because of Princess Luna's endorsement. Even now, the teachers don't like working with her and Junior has been the only one teaching her anything useful. He sighs and agrees to do the exams while she works on finding a counterspell. He then asks why she keeps talking weird and she says she is talking like her mother when she is working.
In Neighpon, Chibi Moon's mother Mariner Serena Moon battles a monster called a baku. She has pale fur and a golden mane in twintails like her daughter and wears a tiara. Serena, talking melodramatically, says normally baku are good creatures that eat nightmares, but this one has gone rogue by eating the ambitions of sleepers. She says she will punish him and hurls her tiara at him, but she convulses with magical energy. Her aim is off, and the tiara boomerangs back and smacks her in the head, knocking her down. The baku approaches, but a rose gets thrown between them. The rose electrocutes the baku, causing it to run away. Chibi's father Ensemble Darien Shroud, who has grey fur and wears a cape, top hat, and domino mask, cradles Serena and asks if she is okay. They look at her Cutie Mark and are shocked to find the former full moon is waning and her power is diminishing. Normally, this was only supposed to happen when Chibi was a grownup and ready to succeed her. Serena says she knows Chibi did something. Their daughter is so grounded.
