(This is for the fanfiction "Crossover Together". Info may change from canon information)
Celestia is described as a very beautiful and regal woman with fair skin and a slim figure. She wore a white cream, long-sleeved dress which ended in a yellow flair at her feet, a set of yellow heeled shoes, accompanied by small gold accessories on her wrists, elbows, and running around her neck and shoulders, a purple gemstone at the center of her chest. Her hair flowed down her back in a flow of many colors, a calming rainbow almost like the aurora lights, and her violet eyes greeted them with calming demeanor and almost motherly comfort. The angel was clearly recognized as such by her creamy white wings, and a horn that came out of her head like that of a unicorn. The horn was also accompanied by a tiara, which was also gold and having a purple gemstone on it.
Celestia used to be the instructor towards Sombra. When Sombra first reported to her about the pollution being caused by the Humans, Celestia made it a point that they can't show themselves to just anyone, according to the laws of deities. When told about an angel being shot at though, she stated that their influence on the Humans was the best they could do, and that the shot was nothing more than an accident. Later on, Sombra reported to her about the looming threat of Tirek, but Celestia still refused to directly involve the fleets, as she felt confident that Tirek would not do anything too drastic. When Sombra left, she promised him to not reveal anything of his former involvement on Elysium.
While not appearing, a spell book Yugure Kagayaki had was first shown, being written by Celestia herself.
Celestia requested Heine Wittgenstein directly to go down to the Surface World for Team Harmony to come by. By the time they finally did arrive, Celestia admittedly felt humbled upon first seeing them, mainly because they all were so young and yet they've done so much. She took note of Sebastian Michaelis, and stated that a Demon was in the throne room, but didn't see him as a threat to her due to reports. As she got to know Team Harmony, she had Winry Rockbell join them. She assigned them as well to help find some bothersome individuals: Great Tengu, Aleistor Chamber, and the Slicer Brothers.