Cinderstasia

Cinderstasia is the family ship between Cinderella and her younger stpesister Anastasia Tremaine from the Cinderella fandom.

Cinderella (1950)
Cinderella and Anastasia are stepsisters, along with Anastasia's older blood sister Drizella Tremaine. The two became family after Cinderella's father married their mother, Lady Tremaine. When he died Anastasia lost another father, but had gained a maid when her mother made the decision to make Cinderella their servant girl, instead of treating her like family. Over the years Anastasia and her family were mean towards Cinderella and didn't viewed her as family, while Cinderella's kind nature has her holding no resentment towards them. On the night of the royal ball, however, Anastasia saw that Cinderella's dress has her sash sowed onto it and tour it off as both she and Drizella ruined Cinderella's dress. So she couldn't attend the ball with them. With help from Cinderella's Fairy Godmother, however, Cinderella's new dress and her dancing with the prince in a far off distance prevent Anastasia from recognizing her.

The next day, Anastasia didn't know why Cinderella seemed distracted until the glass slipper was perfectly placed on her foot and left to be with her prince.

Cinderella II: Dreams Come True
After the events of Cinderella's happy ever after and had began to live in the castle with her prince, Anastasia had began to wonder if she too would be able to find and be with her own prince charming, like her stepsister has done, as she watched the two small figures of Cinderella and Prince Charming twirl around in her music box. With another ball approaching, that the Tremaine family are invited to along with many others, Lady Tremaine wants her daughters to use it as an other opportunity to find a wealthy husband, since they had failed with the prince, they go to the village so they could get themselves new clothes and other fancy accessories to help them. Cinderella had also decided to do some shopping in the village, while wearing her old servant girl clothes to blend in with the other villagers, where she sees Anastasia and the Baker falling in love with each other and decides to get them together; after Lady Tremaine had forced her youngest daughter to leave the bakery. Since the help from both her Fairy Godmother and animal friends is what allowed Cinderella to be with her true love, she wanted to do the same for Anastasia.

Cinderella's well meaning plan, however, didn't go as planned and had made Anastasia look like a laughing stock, along with her bursting into tears over it. Even though Anastasia was mean to Cinderella as she stated how Cinderella's old clothes made her look, Cinderella didn't let it stop her from reassuring Anastasia that there is still hope for her and the baker to be together, once they had her cleaned up and got her into a different dress. Because Anastasia had grown up under her mother's saying and point of view that "looks count as everything", she didn't fully understand why Cinderella wanted her to have a simple pretty look instead of an over the top stunning look, but she came to accept it in the end. Along with Cinderella's advice of approaching the Baker with a smile, which she had little trouble with, and that she shouldn't let her mother's orders stop her from following the choices of her own heart.

The next day, the two met up in the village before Anastasia goes to see the Baker, while Cinderella waits for her at the apple cart. Due to a misunderstanding, however, Cinderella sees Anastasia crying her eyes out, again, and tries to confect her, but Anastasia dashes off and a passing cart prevent Cinderella from being able to do so. When Cinderella finally caught up to her, she sees Lady Tremaine and Drizella telling Anastasia off for her wanting to be with the Baker and how she chose to dress herself, until Anastasia stood up to her mother. Cinderella was pleased to see this, from where she secretly watches them, and as two cross paths with each other at the ball, Anastasia hugs Cinderella as she thanks her stepsister for her help. To which Cinderella tells her that "dreams do come true".

Fanon
After the second Cinderella film showed the short story of them becoming close, despite how cruel the younger stepsister was to the titled Disney Princess, along with the altered timeline in the third film having Anastasia choosing her stepsister over her blood family, fans began to support their sister bond.

Fandom
FAN FICTION
 * Cinderella/Anastasia tag on AO3
 * Cinderella/Anastasia tag on FanFiction.Net

Trivia

 * Even though the two were able to become friends and true sister in the Cinderella tribology, the Descendants novel series has Anastasia as one of the many trapped Disney villains on the Isle of the Lost, with her mother and sister. This could mean that the sequels/spinoffs of Disney films don’t exist in the Descendants Universe.
 * In Sofia the First, Cinderella helps the young title character to become close with her own stepsister as she her song, "True Sisters", has Cinderella telling Sofia of how much she wanted to be close with her stepsisters and leaving them made her sad.
 * A few of the Disney short stories of Cinderella has her being nice towards both of her step sisters.