What if Princess Luna was an alicorn spirit..?

Into the Everfree of Fireflies' Light tells the story of a young filly named Twilight Sparkle and her friendship with Luna, a strange pony with its fake look, who she meets at a young age in a forest near her big brother's home. Twilight learns that her friend is very fragile and that touching Luna will cause her to disappear forever. Twilight returns every summer to spend time with Luna, and their relationship matures as both struggle with its limitations. 

This story is a crossover of a beautiful manga/anime Hotarubi no Mori e, written by Yuki Midorikawa. All of the credit goes to her.

Picture made by me. The original vector belongs to the amazing One and Only - 90Sigma on DA.