Twilight came out of the human world, for the first time. After all the greetings with her friends, she decided to lock the portal by now. Nobody asked why, since she is a princess, she has the power to command without being questioned.
But Celestia did.
While Twilight walked through the hallway to the exit, Celestia joined her in the walk:
"Dear princess Twilight, won't you join your human friends out there as well?"
She stopped. Celestia did the same. Twilight closed her eyes, and forced her forehead as if she was about to cry:
"I... I don't know, Celestia... I'm afraid I end up forgetting my original friends..."
"But you already learnt about the magic of friendship. And you know you can't stay there forever."
"Why? I mean, you never told me about this before..."
A guard stopped the conversation.
"Your highness!", he said, stuttering, with a bow.
Celestia smiled. "Good news, or bad news?"
The guard shook his head. "N-None... N-No Ne-Ne-News..." and a heavy breath.
"Relax. So what do you want to tell me?"
He breathed deeply, and said, with hiccups and very fast inhalation: "Well, P-Princess... Celestia... W-We, the, the, the guar-ar-ds..."
Celestia cast a spell and he said normally. The guard got scared as he felt his throat change. "We, the guards, had an idea to stop incidents such as the Shimmer incident."
"So what's the idea? And why doing this? As far as we know, only two ponies passed that portal: Me, and Sunset!"
The guard realized talking about the portal in the hallway wasn't a good place to pick arguments. So he invited the princesses to go to the room where the portal is. And when they entered the room, there was a small blackboard with a graph drawn. And a scientist pony appeared, showing the graph to the three ponies.
"Are you seeing this, princesses? This graph, in theory, shows what would happen in a big passing of material. For example, one pony, passing through the mirror, should do nearly no danger to both worlds. The danger I mean, is the amount of energy the mirror needs to suck from the other world in order to keep the ponies who passed the mirror to stay in the other dimension. It's expected to the mirror to drain all the energy of the other world in ten thousand years. Two ponies would drain all the energy in a hundred years. Three ponies would drain all the energy in half of a year, and four ponies would end the other universe in 6 hours."
"So if the time is over, the other world is over? What would happen after that?", said Celestia, with a serious face.
"We don't know, Celestia. All we know is that letting ponies walk inside the portal is dangerous to the universe. You know, anypony can reach this room, and those guards... They don't even know what they are doing here...", the scientist said, angering the guard pony.
"So what you want is a better security system?" Said Twilight, curious. "I've already locked the portal. Isn't that enough?"
"Locking the portal only prevent some...thing out there to come to Equestria. Even a foal can unlock this stuff." He said sarcastically, not as if a foal really could unlock the portal. The lock was nothing but a weak magic shield, that physical force could break, or a simple magnet.
"So what do you want to use to protect the portal?" Twilight asked to the scientist.
"Well, I want... A big padlock. A safe, and some chains to put the mirror in. Nothing too scientific..."
"We will provide you everything you need to block the path to anypony who might enter here. Just... Don't take things soooo seriously, you know."
"I'll do my best, Princess. Don't worry. Well, thanks Celestia for your appearance here, as well as Twilight." Then the scientist bowed, and the princesses walked out the room, followed by the guard, who said furious to the scientist: "I know what am I doing here." As the guard closed the door, the scientist waited a few seconds... And started to laugh.
Twilight, however, wanted to be alone, and told Celestia about it. With a nod, she flew to her tower.
"Well, I already visited my kingdom, visited Celestia, Luna is sleeping, Cadance is busy... There's nothing to do today. Where's Spike? Shouldn't he following me? Oh, he must be going after Rarity again... Forget it. As if he was important enough to me care about him now. I'll just go back to my kingdom again. Just to see if they need help on something."
And she flew away...
The fact is that Twilight spent more time inside her kingdom than expected. Instead of flying straight, she needed to visit some towns owned by her, to greet her subjects. That's what she needed to do by now. To everypony notice who is on command.
When she finally got back to the castle, it was night. She was very tired, and she wasn't even doing enough business. Walked to her room, turned the lights off, and said: "Awwww... ful." and she slept.
In the next day, bad news woke her up. Spike was back in the room, almost falling asleep, with a letter in his hand. And... Spike fell asleep.
Twilight investigated the content of the letter.
Dear Princess Twilight,
Please hurry up. Somepony broke through the security system, and no one knows who did it. I need your help.
From Celestia.
Twilight was surprised. "Who could brake through the security system? And how?", frustrated. She thought about flying there, but as she knew she would get very tired, she took a train instead. The train would take lots of time to come, but it was better than sore wings and more hours of resting. The train stopped right next to the castle. She walked to the entrance, and Celestia was waiting for her right there.
"Follow me, Twilight.", Celestia said, serious, walking to the stairs.
They entered the portal room.
