Yumemisaori

Canon
Saori is first introduced when Yumemi Yumemite is in the restroom washing her mouth and hands after talking with the president of her fan club. Knowing that Yumemi hated her fans, Saori recommended that they leave if she was feeling uncomfortable about what she was doing. Yumemi declines saying that she must get to know her fans on a personal so that she will have support from die-hard fans.

When Yumeko Jabami and Ryota Suzui came, Saori wanted to check them for hidden cameras or similar devices. Little did she know, that Yumeko secretly planted a recorder on her. When Yumemi later screamed about her horrible fans, Saori was shocked to see it recorded. She offered to do anything for Yumemi but couldn't deal with Yumeko. After their game she is as devastated as Yumemi, fearing her career is now over. But luckily it wasn't and Saori also pointed out that Kaede Manyuda most likely sabotaged the game. She was angry at him for selling Yumemi out like that. But she was still very relieved, her career wasn't over.

Kakegurui XX
Saori helped Yumemi Yumemite in the election as much as she could, for example by getting all the votes from her fans. After that she suggested she should starts gambling herself again. She was shocked to hear that Kawaru Natari was at the school, but of course wanted to support Yumemi through that battle. She stated, that Yumemi had to win no matter what. That's why she and Yumemi bribed the audience so they would vote for her during the singing contest. Ryota Suzui though that Yumeko Jabami must surely be against that, but Saori saw it as necessary. When Yumemi still lost, she was devastated.

In the second round, Saori quickly realized that Yumemi must have broken her own finger in order to fake a reaction. That made her very sad, but she was so relieved that this round at least ended in a tie. During the third round Saori almost is close to tears, when she realizes Yumeko isn't working with Yumemi anymore. But Yumemi looked at her and Saori was hoping so much for her win. Yumemi remembers when her idol-career started thanks to Saori.

Yumemi was determined to become an actress and didn't think that becoming an idol would help. But Saori has always been affectionate towards Yumemi and declares that she always wants to be by her side and will support her through everything. Together, they started Yumemi's YouTube channel and Saori experiences her rise in popularity. She was so proud when she was accepted on the Student Council. Saori was always there for here and just wants her to be happy. This made Yumemi realize, that being an idol is worth so much to her and she doesn't need all the fame. Due to this Kawaru ended up losing and it made Saori indescribably happy to see Yumemi not only win, but also accept herself as an idol.

Other Kakegurui Media
In an omake, Saori is seen getting visibly protective of Yumemi when Sumika Warakubami gets too close. The two have also been seen getting very close in official art.

Fanon
This ship is not the most popular, as Saori is a very minor background character. It is rivaled by ships such as Simuka and Yumemi, and Yumeko and Yumemi. Many fans love the trope of the "plain" girl and the flashy cheerful girl.

Fan Fiction
Yumemi/Saori tag on AO3

Tumblr
YumeSao tag on Tumblr