Sion works as a waitress in a restaurant Kukai had been going to ever since he was a kid. Nadeshiko says the restaurant looked like one that would be in an American movie.
Sion is shown with light brown hair, and a light shade of brown eyes which look kind of purple. Her hair is pinned up like a bun with some hair hanging down that just barely reaches her neck. She also has bangs with a split off on the left side of her face, so she has bangs on either side of her face. On the side of her hair are some pins, keeping her hair from falling out of line.
Her waitress outfit consists of very light shade of pink shirt with a nametag to the left side, a brown skirt that is a lighter brown near the bottom of it, and brown high heels.
Sion is the friend of Kukai, having known him since he was born. She works as a waitress in a restaurant, the place Kukai says he had been going to ever since he was a little kid. Kukai tells his friends a day or two after they met Sion that she was going to turn nineteen the following week. That means she was eighteen when she first met Kukai's friends, though it is not certain she turned nineteen in the episode because Kukai never specifies her birthday and nor do they wish her a happy birthday on a certain day.
When she meets up with Kukai at a spot they hadn't visited together in awhile (a grassy area right next to a river), she tells him she was going to be leaving the city to go to a music school where a piano teacher she respected taught. She told him she wanted to see how far her music would take her and Kukai tells her it was a great opportunity, but he notices that she didn't seem very motivated.
While passing through the mall after meeting up with Amu and Kukai, Sion comes upon a Utau Hoshina concert. She sees Utau and is in awe listening to her. Then Utau extracts the heart's egg from the crowd, including Sion's, and turns them into X-Eggs. Without her heart's egg, Sion bashes her piano playing, saying it wasn't any good. When she gets it back, though, she wonders what the awful feeling she had just felt had been.
The day she was to leave, she was waiting outside the train with Amu for Kukai, who was running late. Sion tells Amu it was time for her to go and thanks her for showing up, but Amu tries to stop her. Someone calls her name and they see Kukai running toward them. He's covered in dirt and out of breath, and when he gets it back, he pulls out her farewell gift and birthday present: a four-leaf clover. Ran makes the connection that he was late because he was looking for it and Daichi, also covered in dirt, says that he and Kukai had a hard time finding it.
Sion hugs Kukai, much to his and Daichi's shock, but to Amu's delight. She boards the train and Amu waves at its retreating form before turning to Kukai, seeing him in a shocked state. She wonders if it was love he felt for Sion after all, breaking him from his shocked state. He tells her that maybe it was. On the train, Sion is still admiring the four-leaf clover with a slight blush on her face and thinks that Kukai was going to be a good one.
- Kukai Soma: Though at first they acted in a sibling manner to each other, it is shown that Sion may have felt something more towards Kukai as she is seen blushing a little at the gift he went through a lot of trouble to get for her. She is also close with Kukai's parents and has known him and his older brothers (Kaidou, Shuusui, Unkai, and Rento) for a very long time.
- Amu Hinamori: Though Amu and Sion weren't very close, they are shown to get along well; Amu likes Sion's piano playing like others who have heard it, too. Amu even tries to help Kukai find a farewell present for Sion since it meant a lot to him when she could've been off shopping somwhere. She also comes to see Sion off when she was about to leave for a music school.
- Nadeshiko Fujisaki: Nadeshiko and Sion didn't know each other very well, but they are shown to get along when they first met; Nadeshiko, like others, enjoys hearing Sion's piano playing. Nadeshiko even teams up with Yaya to try and make Sion Kukai's girlfriend, even though Kukai kept telling them Sion was like a sibling to him.
- Yaya Yuiki: Yaya didn't know Sion very well, either, but she is shown to get along with Sion and enjoys listening to her play the piano. Yaya likes it so much she tries to play the piano in the music room at her school, but she wasn't very good. She says that Sion looked cool playing the piano and she wanted to give it a shot. Yaya teams up with Nadeshiko to try and make Sion Kukai's girlfriend and tells Amu that, when dealing with love, age didn't matter.