Perhaps in the fanfic, Luna has a nightmare about her past as Nightmare Moon. She wakes up crying because she fears that she could lose control again and turn back into that evil form. This would show her internal struggle with her own identity and the fear of repeating her past mistakes.
One possible plot could be that Harry is lost in the MLP world and Luna is the first to discover him. She helps him adapt to this new world filled with ponies, and as they spend time together, they start to fall in love. Along the way, they might have to face some villains from the MLP world who don't like the idea of an outsider like Harry being there.
Show the reactions of other characters. If the other ponies in the fanfic see Luna crying, their reactions can enhance the emotional atmosphere. For example, if they are sympathetic and try to comfort her, it shows that Luna is loved, but if they are indifferent, it makes her situation even more pitiful.
Well, one possible plot could be that they start as enemies as in the original lore. But then, an external threat forces them to work together. They gradually learn about each other's pasts and find some common ground. Maybe they both had difficult upbringings in different ways. And in the end, they form an unlikely alliance that changes the power dynamics in Equestria.
The plot could revolve around a competition. Prince Artemis challenges Princess Luna to a series of tests to prove which one is more powerful in controlling the night - related magic. As they go through the challenges, they start to respect each other more. In the end, instead of a clear winner, they realize that by working together, they can achieve even greater things with their magic.
Well, it could be that Luna, from My Little Pony, gets into some kind of danger in a world where Naruto also exists. Maybe there are dark forces threatening Luna, and Naruto, with his ninja skills and sense of justice, decides to protect her. He might use his shadow clone jutsu to surround and guard her, or his rasengan to fend off attackers.
Well, it could be about a girl named Sakura who is crying because she lost her pet. She might be wandering around the sakura trees, reminiscing about the good times with her furry friend. The story could focus on her journey to come to terms with the loss.
In the fanfic, Princess Luna's daughter might have a special role in the annual Nightmare Night celebration. Since it's related to Luna's past and the idea of facing nightmares, she could add a new element to it. Maybe she creates a new kind of spell that allows ponies to face their deepest fears in a safe way during the celebration. She could also befriend some of the more outcast ponies in Equestria, those who are often overlooked because they are different. Through her friendship, she shows that everyone has value, no matter how strange they may seem, and in turn, they help her grow and understand different aspects of Equestria.
It could be about Luna's feelings of isolation. In the MLP world, Luna was once banished, and a fanfic could explore her lingering sadness from that experience. Maybe she still struggles with being accepted fully by the ponies, and the story delves into her inner turmoil.
One key element is Luna's character. Since she's a complex character with a past of being Nightmare Moon, fanfics often explore her redemption and her relationship with the other ponies. Another element is the magical world of Equestria. Fanfics use this setting to create unique stories around Luna, like her connection to the night sky and moon magic.
It could be about a young pony who has lost something dear, like a special friendship or a magical item. But they don't want others to see their sadness, so they keep it to themselves and try to be strong when the sun is out (which could represent the public eye).