On the small shore right outside the Tower Mastery in Shalour City, a young boy asks his elder brother what 'mastery' means in the tower's name. The elder boy, probably in his teens at most, replies that 'mastery' means 'guru', and whoever climbs this tower becomes a guru. The younger boy questions what kind of guru they become, but the elder boy apparently has no idea either. The two then decide to leave, as their mother is probably waiting at home.

Standing at the doorway of the Tower, Gurkinn overhears the boys, and muses that times have certainly changed since not even the children of the city know the truths about the building anymore. He mutters to himself that this may be for the best, and turns around to walk into the lobby of the tower, where a giant Mega Lucario statue is erected. Long ago, it was the ancestors of Gurkinn who first discovered Mega Evolution in the Kalos region, and their clan has been responsible for passing down its knowledge for generations. In a sense, the secrets of Mega Evolution have remained within their clan all these years, and Gurkinn seems quite proud about it. He looks up at the Mega Lucario statue, and voices out his pride for being one of the limited few who possess the knowledge. However, he is soon attacked by Korrina, who appears out of nowhere and kicks him hard on the head. The girl gets into fury, and cries that Gurkinn has hardly kept the secrets within their clan by leaking it to outsiders.

Gurkinn holds his swollen head in agony, and wants to know why his granddaughter is hitting him. Korrina snaps that there is no grandfather and granddaughter while they are inside the tower, as she is merely a disciple and Gurkinn her teacher, something which the old man taught her. Korrina tells Lucario to get ready to Mega Evolve to give another strike, but Lucario clearly feels distraught and is hesitant to move. Gurkinn intercepts Korrina from activating her Key Stone just in time, and begs her to tell him what exactly happened.

Korrina angrily recalls that Gurkinn has always said that Mega Evolution is not something that should be taken lightly, and that his task is to confer this knowledge to the appropriate, qualified and recognized person through a formal successor ceremony. Gurkinn affirms her saying, but still doesn't see what the problem is. Korrina then confronts him with the photo of X, taken by Viola at Santalune City, and demands to know why the boy was an exception.

Gurkinn easily recognizes X although he was just a little boy when they met, and finally makes sense of Korrina's anger. He states that X is a trainer of true skills, and beckons his granddaughter to follow him into the chamber beneath the Mega Lucario statue. Inside, he shows her a recording of the Kalos Junior Tournament few years ago, which featured the final match where young X claimed championship after beating a Noivern with his Kangaskhan. Since his first match in the Tournament, X has displayed unparalleled skills, and overwhelmed every single one of his opponents along the way.

It turns out that Gurkinn was one of the narrators of the tournament, and both he and the announcer were at a loss the words that could adequately describe the boy's talent. They looked forward to his growth and development, however, and believed that with his ability, X could easily become a Gymleader or even a member of the Elite 4 in the future.

Korrina still fails to see how the recording justifies what happened, and Gurkinn states that X won him over not only due to his achievement, but also the electrifying aura he exuded when he battled. He recalls that the boy also suffered from the troubles that arose from his strength, which sadly is always one negative impact of being strong.

Back then, X was chased around by the paparazzi after the Tournament, and the boy tried his best to hide after being frightened by their eagerness on stage, which nearly crushed him and his four childhood friends. When X finally found a quiet corner to take a breather, he was unfortunately discovered by two reporters. The two men forced his exhausted Kangaskhan and child out of the Pokeball just to take photos, and being a young kid, X didn't have the physical strength to stop the men and could only watch as his companions suffer. At that moment, Gurkinn came to X's rescue and gave the two reporters a good beating. He counseled the young boy, and urged him not to become hateful just because being with his Pokemon drew bad adults near. On the contrary, he should always treasure the bond he shared with his Pokemon and trust their companionship. Gurkinn gave X the Mega Ring at that point and hoped that it would serve as a reminder of what he said.

Even today, Gurkinn feels a little proud of his heroic act in saving the young boy from the bad people, not to mention the profound and timely speech he gave. He is about to say how electrifying the boy's battle style was again, but Korrina angrily kicks him in the face, and hollers that he still hasn't addressed her question. She reiterates that she isn't challenging Gurkinn's decision to choose X as a successor, but just fails to understand why he passed down the Ring without having a proper successor ceremony. She finds it unacceptable that Gurkinn would contradict his usual sayings and pass down a Key Stone so light-heartedly, regardless of how strong or talented a trainer is.

Gurkinn runs around the room and begs his granddaughter to stop when he suddenly feels a sharp pain on his left shin and falls to his knees. Korrina gasps in astonishment, and apologizes to her grandfather. However, Gurkinn points out that it isn't Korrina's fault, and shows her a cut on his shin, which appears to be made by some kind of twig. At that moment, Korrina notices the half-open door, and catches a glimpse of something fast moving outside. She realizes that they have an intruder, and quickly darts out of the chamber with Lucario while telling her grandfather to stay inside.

Korrina chases after the silhouette which is moving up the spiral stairs, and wonders if it is targeting her or Lucario. Whatever the case, she is determined to teach it a good lesson, and raises her left hand with the glove that holds the Key Stone. She places her right index and middle fingers onto the stone to activate it, and instantly Mega Evolves Lucario. The intruder reaches the exit to the balcony upstairs, and Korrina demands it to stop and show its face. Mega Lucario hops between the stair rails to quickly gain height, and manages to catch the silhouette before it slips out, revealing it to be a monstrous tree with one single flaring red eye. Korrina exclaims that it is Trevenant, the elder tree Pokemon of the ghost and grass type, and realizes that it probably used its many twigs to attack her grandfather with a Horn Leech earlier.

As Mega Lucario engages into combat with Trevenant, Korrina notices that its trainer is nowhere to be seen. She recalls seeing two shadows outside the door downstairs, and assumed that one must be the Pokemon while the other its trainer. She reaches the balcony floor herself, and goes outside to inspect, but still finds no trainer. At that moment, she bolts with realization that the enemy isn't targeting her or Lucario, and neither the Key Stone nor the Mega Stone, but her grandfather instead. She tells Mega Lucario to handle Trevenant while she returns to Gurkinn, but discovers in horror that the spiral stairs have been destroyed, cutting off her access to the lower floors now.

Down on the ground floor outside the chamber beneath the statue, Gurkinn stays alert as he is approached by a mysterious young woman in black and orange suit wearing a full helmet that has the character 'E' on the face shield. She is accompanied by a Phantump and speaks in a mechanical tone. The young woman wonders how tall the Lucario statue is, and Gurkinn replies that according to his own grandfather, it is 12 meters in total, about 10 times the size of a real Lucario, but if the stage it stands on is counted, it probably measures up to 15 meters.

The mysterious trainer thinks it must be a symbol of power, and Gurkinn smirks that it sounds like she wants it for herself. The young woman wants to know if Gurkinn also once wielded Mega Evolution himself, and Gurkinn makes no attempt to hide the fact. He remarks that his ancestors were the first to discover Mega Evolution and Kalos, and naturally the descendants would inherit and pass it on. He recalls a time when he was surrounded by many who could wield Mega Evolution, and how everyone sought out the Mega Stones in order to Mega Evolve their beloved Pokemon. Of course, there were also people with ill intentions who were after Mega Evolution, but he made sure that they never got their way.

The suited trainer remarks that such seekers of Mega Evolution are nowhere to be seen no, and not even the residents of the area knows about it anymore. As for Gurkinn, he has essentially become a hermit now and only passes on Key Stones to those he recognize. Gurkinn snickers that this should make things convenient for the young woman and her comrades since no one else but him has the authority to confer Key Stones and the skills to create items like rings or gloves for setting the Stones. In other words, they simply need to capture him alone to gain everything about Mega Evolution.

The young woman is glad that Gurkinn has already figured things out, and says it is time that he goes with her. With that, she cries out 'Mission Starts!! Target: Gurkinn! Expansion!!' and calls forward her Phantump to attack. On the upper floor, Korrina watches in horror as the enemy approaches her grandfather…