One possible plot could be that Rarity contracts a rare and incurable disease in Equestria. Her friends, like Twilight Sparkle, would try everything to find a cure. But in the end, she passes away peacefully, leaving behind a legacy of her beautiful creations. This could show how the other ponies deal with grief and remember her through her works.
Maybe in the fanfic, Rarity sacrifices herself to save Equestria from a great danger. For example, an evil force is about to destroy the whole land and she uses her magic and unique skills to stop it, but at the cost of her own life. Her death then becomes a symbol of heroism, and the ponies hold her in high regard forever.
One possible plot could be that Rainbow Dash gets into a dangerous race and has an accident that results in her death. Her friends then have to come to terms with the loss and remember all the good times they had with her.
One possible storyline could be that Spike's death has a profound impact on Twilight Sparkle, leading her into a deep depression. She might struggle to carry on with her studies and magic without his constant support.
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.
Perhaps in the 'naruto dies narusaku fanfic', Naruto sacrifices himself to save Sakura from a powerful enemy. Sakura, in her despair, starts to discover new aspects of Naruto she never fully realized when he was alive. She could then start a journey to find a way to bring him back, encountering many challenges along the way and meeting old friends and foes who either help or hinder her.
Maybe in the fanfic, Aunt May's death is the catalyst for Peter to take on a more serious and darker approach to fighting crime. He could start to question his no - killing rule more severely. For example, he might face a villain who was directly or indirectly responsible for Aunt May's death and be on the verge of crossing that line.
One possible plot could be that Ruby is facing an overwhelmingly powerful enemy alone. Despite her best efforts, she is mortally wounded in the battle and dies heroically. Another could be that she sacrifices herself to save her friends from a deadly trap or a powerful Grimm attack.
One possible plot could be about how her friends deal with the grief. They might gather to remember the good times they had with her, sharing stories and mementos.
One possible plot could be the ponies in Equestria struggling to come to terms with the loss of their beloved leader. They might face challenges in maintaining order and harmony without her wisdom and guidance.
I'm not entirely sure as it seems like a very specific and rather odd concept. 'MLP FIM' stands for 'My Little Pony: Friendship is Magic'. But 'rarity butt inflation fanfic' sounds like a made - up and strange fan - created story that likely involves some sort of comical or perhaps inappropriate (if taken too far) inflation concept related to the character Rarity. However, without actually reading it, it's hard to say exactly what it's about.
I'm not sure specifically as there could be many different 'My Little Pony' fanfics where Celestia dies. It could be about the reactions of the other ponies in Equestria, like Twilight Sparkle having to step up in a new way without Celestia's guidance. Maybe it also explores how the balance of day and night is affected if Celestia is no longer there to control the sun.