One idea could be that the OC is a new student in the killing game. Celestia initially sees the OC as an easy target to manipulate but gradually finds herself intrigued by the OC's unique personality. They could form an unlikely alliance where they work together to solve the mysteries of the game, and in the process, Celestia starts to develop real feelings for the OC.
Character development is key. For Celestia, show how her relationship with the OC changes her. Maybe she becomes a bit more vulnerable or starts to question her own actions. For the OC, show how they grow in this dangerous and strange environment with Celestia by their side. Also, use dialogue effectively. Celestia has a very distinct way of speaking, so mimic that in your writing. And don't forget to have a clear plot structure. Start with an introduction that sets up the situation, have a middle part full of rising action and relationship development, and end with a satisfying conclusion, whether it's a happy ending or a tragic one depending on the tone you want to set.
You can try fanfiction websites such as Archive of Our Own. It has a large collection of various fanfics, and there's a good chance you'll find some great Celestia Vega ones there.
Another place to find Celestia fanfics is FanFiction.net. It has been around for a long time and has a huge database of fan - created stories. Just search for 'Celestia' in the search bar and you'll likely find a bunch of relevant fanfics. However, the quality can vary, so be sure to read the reviews or summaries first.
You can try looking on fanfiction websites like Fimfiction. It has a large collection of My Little Pony - related fanfics, and there's a good chance you'll find some Celestia Lemon fanfics there.
Archive of Our Own (AO3) is also a great place to look. It has a wide range of fanfics from various fandoms, and its tagging system makes it easier to filter for Celestia Changeling fanfics. Just type in 'Celestia' and 'Changeling' in the search bar and browse through the results.
Celestia is known for her wisdom and grace. She is very powerful as she is able to raise the sun every day. She has a kind and patient nature, always ready to guide her subjects. Luna, on the other hand, is more mysterious. She has a connection to the night and the stars. Once she overcame her dark phase, she became a symbol of the night's beauty and tranquility.
They can change her appearance. Maybe make her look more menacing, with darker colors in her mane and tail, or a more stern expression. For example, her eyes could be drawn to look cold and unfeeling.
In fanfic, 'anthropomorphic Celestia' means presenting the character Celestia in a human - like form. It gives her more relatable human characteristics and behaviors, which can be used to explore different storylines and relationships within the fan - created narrative.
Fanfiction.net is another good place. There are many users who post their fanfics there. Just use the search function and type in 'twilight x celestia fanfic' to see what comes up. However, the quality can vary, so you might need to do some sifting through the results.