Back at Canterlot, moments before dusk.
Princess Luna was sound asleep having a pleasant dream of a beautiful field of moonflowers at night. As she was trotting along she could faintly see something in the distance. When she flew over to it, she saw it was a door with an illustration silver gem with a light blue highlight on the center. Luna placed her hoof on the illustration which caused the door to open be splitting into five segments. Past the door was a dark room with blue crescent moon lights on the top of the walls and stars on the celling twinkling with a chandelier with silver lights on the center of the roof. "What is this place and why does it feel like I've been here before?" Luna asked herself. As she continued to walk through the room, she noticed a round object at the end of the room slightly floating above a pedestal. She went closer to inspect it and saw it was a blue and silver bubble with shards of a yellow gem inside. Just then, without reason, tears started to run down Luna's cheeks. "How... how am I crying? I don't even know this place. Or, do I?"
"Luna, are you alright? Please, wake up," Celestia said trying to wake her sister up. As Luna wakes up, she notices the tears that were streaming down here face.
"Sister, was I... crying in my sleep?" Luna asked.
"You were like this when I came in. What happened in your dream?"
"I don't know, I was inside a room that somehow felt familiar even though I've never been there before." Luna then wiped the tears off her face and got out of bed. "I shouldn't worry about it now. I have my responsibilities to oversee." Luna then proceeded out the room with Celestia following close behind to begin the night. After the sun had set and the moon had risen, Celestia went to bed while Luna used her magic to enter the dreamscape. She began doing her usual routine of checking for any nightmares. She went further and further into the dreamscape until she almost reached the end where she noticed something in the distance. Closer inspection revealed it was the same door from her dream. "This again? What is this door?" Luna asked as she began looking at the door more closely. She placed her hoof on it again which caused the door to open the same way. Luna stepped inside the room, but then flew over to where she saw the bubbled gem shards and just as she reached it, she started crying once again. Despite her tears, she wanted to inspect the shards more. When she got closed to the bubble, she unconsciously said, "Sunstone."
"Luna, are you sure about this?" Celestia asked as Luna was preparing to leave the castle.
"I must find out more about that room and why it feels so familiar. I'm not completely sure, but I feel it has something to do with Sunstone and Moonstone."
Celestia then nodded and said, "Very well, just return safely." Luna then gave Celestia a hug before she took off to the Gem Temple. The temple soon reached her field of vision and then she descended to the entrance which she knocked on. The door opened and revealed Red Pearl on the other side.
"Oh, uh, Princess Luna. What brings you here?" Red Pearl asked as Luna walked inside.
"I need your help. Is there anything in here connected to Moonstone?"
"Moonstone? I could take you to her room." Red Pearl escorted Luna to the door of Moonstone's room which looked familiar to her.
"That door, the same door I keep seeing," Luna said.
"The same door you keep seeing?" Red Pearl asked.
"The reason I came here. I saw this door in both my dream and in the dreamscape and every time I enter the room, there is something in there that makes me start crying," Luna responded. She then placed her hoof on the door which made it open the same way it did in her dream and in the dreamscape. The princess and the gem then walk deeper inside the room until they reach the end. Luna already knew what she would find: a blue and silver bubble containing the shards of a yellow gem. As expected, tears start streaming down her cheeks again.
"Your Highness, are you feeling okay?" Red Pearl asked concerned.
"Red Pearl, what can you tell me about the gem inside?" Luna asked.
Red Pearl frowned looking at the shards as she said, "Those are the shards of Sunstone. Ever since she got shattered, Moonstone kept her shards inside one of her bubbles and stored it inside her room as a keepsake. She was the one most devastated from Sunstone's shattering. Is this the reason you wanted to come here?"
"It might be because I have Moonstone's power, I start feeling her sorrow whenever I'm near Sunstone's shards. It would also explain why this room felt familiar even though this is my first time in here," Luna answered
"You're the first one to receive a memory of the gem whose power you have; I don't know how to help you. Is there someone I can get that can?" Red Pearl asked.
"No, thank you, I believe I already know somepony that might help me." Luna then left the temple and started flying back to the castle. Just as she left, Spike came to the door.
"Was that Princess Luna? What was she doing here?" he asked.
"She came because she wanted to know something, but I should tell everyone what she told me," Red Pearl said as she walked back in the temple with Spike following her.