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.
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.
A fanfic titled 'Luna's Redemption in Celestia's Eyes' is quite interesting. It focuses on Luna's journey towards redemption from Celestia's perspective. It shows how Celestia has always believed in Luna, even during her darkest times. The story is filled with emotional moments that really tug at the heartstrings.
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.
First, understand the character well. If you want a pony to cry, you need to know what would break their heart. For example, for Pinkie Pie, it could be something that ruins a party she's been planning for a long time. Then, describe the build - up. Show the events leading to the crying moment. Don't just jump to the crying part right away.
Some mlp crying fanfics focus on the ponies' past traumas. For instance, Rainbow Dash could be crying as she recalls a difficult race in her past where she let her team down. The fanfic author uses the crying as a way to show the pony's growth and how they've overcome or are still dealing with that difficult memory.
One common theme is redemption. Since Luna has had a troubled past with her banishment and all, many fanfics focus on her trying to redeem herself in the eyes of the other ponies. For example, she might be trying to make up for the bad dreams she caused in the past.
One possible plotline could be that Luna sacrifices herself to save Equestria from a powerful and ancient evil. She might use all of her magic and strength to defeat the foe, but in the process, it drains her life force completely.
One common theme is friendship. Since Spike and Luna are from different parts of Equestrian society, their friendship can be explored in many ways. For example, how they bridge the gap between a young dragon and a princess of the night.
Another theme is friendship. Even as a baby, Luna is shown forming bonds with other ponies or characters, like how she might interact with her sister Celestia in a more innocent and playful way. And these interactions help shape her future relationships. For example, in some fanfics, her early experiences with friendship teach her important values that she carries into her later life.