Sonata has straight, shoulder length orange-yellow hair with a small section of it tied into one ponytail on each side and has light orange eyes. She wears a small black hat with bunny ears on the side of her head. In her pre-trainee outfit, she wears a pink hoodie with bunny ears, a white dress with black and blue ruffles, and a pair of black lace-up shoes. Like all the AKB0048's trainees, she has a heart-shaped lining in her hair and eyes.
Sonata is an excitable, immature girl, like most children. She has a passion for adventure and is determined to join AKB0048, even if she did fail the first audition. At times, she speaks in the third person, though not always. She seems to enjoy giving people nicknames, calling Suzuko 'Linda', Makoto 'Grumbly', Chieri 'Meanyface', Megumi 'Nasty', and Yuka 'Demon'. She also has a tendency to say words in pig-latin sometimes such as oobs-bay.
Sonata lived on a desert planet. Sonata used to smile to Kanata's singing. But when their father, who was the leader of a pro-entainment coalition, got killed, Kanata left Sonata behind with her mother in order to join AKB0048 so she can avenge their father's death by fighting DES, the organization responsible for the death of their father. Since then, Sonata wanted to join AKB0048 so she can be reunited with her sister Kanata.
Sonata, unlike the other girls, did not pass the first round of AKB0048 auditions, probably because she didn't meet the age requirement. Unsatisfied with this result, she became a stowaway on the ship en route for the auditions, surviving by stealing food from vending machines. It should be noted that her sister Kanata was not on board with her. She first met Suzuko Kanzaki checking to see if members of the ship's crew had left. She later meets Orine Aida, Yuka Ichijo, Makoto Yokomizo and Nagisa Motomiya when she interrupts their conversation, overhearing that they too want to join AKB0048. Whilst she is at first looked for by the members of the crew, they don't seem to be too concerned about her after the DES attack on the ship and tip-off that Chieri Sono is also on board. She, along with the other trainees managed to escaped the DES thanks to AKB0048 who came to rescue the trainees.
On board the training ship in Episode 3, Sonata tells Tsubasa that she is here to audition, despite being rejected in the first round. Tsubasa smiles at her and says to go ahead as no one is stopping her. Sonata then participates in the grueling training, and goes to the guerilla planet, where she along with her six friends makes it through and become the 77th Generation trainees of AKB0048.
On the homeworld of AKB0048, Sonata is overjoyed to see her sister Kanata in Episode 4, cheering her on in her performance on stage with Mimori and tackling her backstage while squealing "Onee!" over and over. However, Kanata's reception is very cold to Sonata, saying she cannot be here due to the age rule. Tsubasa steps in and informs Kanata that it is her sister's decision, and that she does not have the right to decide Sonata's fate. As Kanata storms off, Sonata is left hurt and wondering why her sister acted the way she did.
Later, Sonata tries to make Kanata warm up by saying she only wanted to spend time with Kanata, but Kanata leaves the room without saying a word to her. Sonata later confronts her in the hallway, and Kanata makes to slap her, but Mimori stops her. Sonata says her sister is a liar and runs away. Later in dance practice, when Chieri criticizes Kanata for her poor performance, Sonata leaps to her sister's defense, scolding Chieri and calling her "Meanyface". Later in the afternoon, as Mimori and Kanata sit singing on the hillside, Sonata appears on the hill alongside her friends and cheers Kanata on. Finally, Kanata gives in to Sonata, and a happy Sonata charges down the hill and hugs her sister before joining in the song.
During Episode 5, Sonata gets Suzuko to join her in the bath, as usually when she fools around in the bath, she ends up being scolded by Kanata. As she frolics in the bath, Suzuko informs her of her thoughts and worries about Sensei Sensei. Mayuyu suddently appears in the bath, and after telling Suzuko a bit about Sensei Sensei, torments Sonata for eating her extra helpings. After a conversation with Yukirin, Suzuko drags Sonata out to spy on Tsubasa with her. Sonata at first protests as she does not want to lose her belly button, but eventually warms up when she finds a cat in Suzuko's hiding place. At the end of the episode, she is sleeping beside Suzuko as Tsubasa and Ushiyama walk up.
In Episode 6, it shows Sonata giving fan mail to Orine, which turns out to be a threat. Later, during the handshake event, Sonata wears bunny ears to the handshake event and tries to use Makoto as a shield, but Makoto strongly refuses.