Saya is a black-haired individual with brown eyes and has a beauty mark on the lower left of her face. Official art depicts her with casual clothing, wearing a pink and brown jacket with an armband with a bear design in her left arm. Also, she wears blue leggings. Her height is 167cm.
When she was younger, she had longer hair, and looked more similar to Black★Gold Saw this way. She wore a sailor school uniform that resembles the school uniform seen in the OVA, but had a red tie instead of blue.
She is calm and gentle, and is generally the go-to person to talk about problems. She is also fond of coffee.
However, she seems to have a strange darker side. At one point, she imitated Yomi Takanashi's behavior in private. When Arata Kohata goes to her after her public shaming in the eyes of the school, she only stares at her flatly, tears trickling down her cheeks, and talks about her being the laughingstock of the school rather than comfort her. She also openly defies Yomi's request for coffee with sugar, giving it to her black instead. Later, she told Yomi that no-one needs Yomi anymore, but then acted like she said nothing.
She also seems to be aware of something more than simply the real world, as Mato and Yomi's names are circled in her student list, and when Black★Rock Shooter beheads the mysterious hooded figure that has a similarity to Arata, she senses it. She also seems to sense Yomi/Dead Master's breakdown in both the real world and Otherworld, calling it a success. Eventually it is revealed that she first merged with her other self to protect the other world and Strength and has been doing so ever since.
She is the middle school counselor at Mato's school, running "Dawn Counseling" at the consultation room.
Mato runs into her on the first day of school, and she tells Mato to come over anytime if she has any problems. When Mato finally does show up to talk about her discomfort about her situation with Yomi, she advises Mato that she will inevitably make enemies as it's a part of life, and that there is someone out there who will take her heart's pain for her.
A few days later, Mato comes back to tell her about her strange dream that she had involving two mysterious girls and a call for help. Saya tells her that dreams are sometimes a way for friends to tell each other things that can't be said in words, and that Yomi might be telling her something.
The next time she is seen, she is watching a dejected Yomi in front of her room, and asks if she wants to go in. Yomi refuses kindly and runs off. While in her room, Saya imitates Yomi's refusal and pulls out a list of students and looks at the page with Yomi and Mato's pictures, both of which have their names circled. Arata later comes in to meet her after being publicly shamed by the school, telling her that she shouldn't do things she's not good at. However, instead of comforting her, Saya only looks at her with a blank expression, some tears trickling down her face and her eyes strangely wide. She tells her that it's okay to cry if it hurts, that she's being strong by acting like this when the whole school is laughing about her, that she's the laughingstock of the school. When Yomi is walking home, thinking about her situation, Saya looks at her from the window and calls to her, inviting her in for coffee. Yomi obliges and, when Saya asks her if she wants sugar, she asks for coffee with two spoonfuls of sugar in it. Saya gives her coffee, and Yomi drinks it, saying it is bitter, and Saya tells her she gave her black coffee.
Suddenly, in the Otherworld, Black★Rock Shooter beheads one of the hooded figures that resembles Arata, and Saya noticeably senses it, her face reverting to the blank state that it was in before and tears tricking down her face again.
When Yomi goes to Saya for help due to both Mato and Kagari distancing themselves from her, Saya simply says that no one needs Yomi, upsetting her, but then pretends she said nothing. This statement causes Yomi to steadily break down as she believes Mato and Kagari no longer care about her, affecting Dead Master as well. When Yomi and Dead Master finally break down completely, Saya seems to sense it and simply mutters, "Success".
Mato is walking in the hallway when Saya asks her if she wanted something to drink. Saya gives Mato black tea instead, saying that she actually hates coffee. Saya then places her tea down, asking Mato if she really wants to save Takanashi. Mato says she doesn't really understand what Saya means by "save", but says yes. Saya says, "Then... I think you should die for her." She strangles Mato but then releases and says she is only kidding. Mato runs out of the room. Saya then says that she suggests that Mato should go to the art room, where something cool is awaiting for her. Saya then mutters to herself, "I don't have to kill you today".
She is later seen in her house following Black★Rock Shooter going insane, as witnessed by Black★Gold Saw . A constant ringing of her doorbell snaps her out of her thoughts, forcing her to answer the door. There she finds Yuu carrying Mato on her back, asking desperately "What should I do?!". Saya slaps Yuu, yelling "What have you done?!", aware that if Mato or any girl bears the entirety of their pain and suffering by linking with their "other" self, that the other selves will lose what little humanity they have left. She seems to then state that she awoke Dead Master by traumatizing Yomi.
Saya avidly states that Black Rock Shooter has the capability of destroying the "Otherworld" if she is awoken, and tells Yuu to imagine what would happen to Mato/BRS if that happens. Believing that the only way to stop Insane Black★Rock Shooter is to kill Mato, Saya proceeds to extend her hands out to strangle her as she had at school. However, unlike before, she is unable to even get her hands around Mato, crying out that Mato had done nothing wrong and shouldn't be punished for it.
The only option left for Saya was to link with Black Gold Saw and try and talk to iBRS to see if she could get Mato to come back and return her to normal. Yuu tries to volunteer for the job, but Saya quickly tells her to remain where she is since her duty is to protect "that girl" which is implied to be Yuu/Strength. In the "Otherworld", Saya tries to talk to Mato, effectively halting iBRS' assault and uses the opportunity to explain the past between Yuu and Saya.
Saya is shown at a younger age, walking to school, and finds a young Yuu walking out of the school grounds, soaked in water. With people looking on and laughing, Saya approaches Yuu and invites her to Saya's house where she gives her noodles and something to drink. Saya goes to look for ice cream, passing by her mother in the kitchen that seems to already know who Yuu is, asking if she was from the Kotari family 3 blocks down. Saya's mother explains that Yuu has endured pain the likes that no one can imagine.
As time goes on, Saya tries her best to become friends with Yuu by greeting her at school, and hanging out with her. Yuu, even back then, still seems to know about the "Otherworld" as well as the existence of her "Other" self which has Saya puzzled as Yuu explains how "she" takes her pain and helps her endure. Later down the line, Yuu's house catches on fire due to her step-father carelessly leaving a lit cigarette behind. Whether Yuu's parents survived is unknown, but after being informed, Saya runs to Yuu's house to find it already engulfed in flames. Not knowing the situation, Saya believes that Yuu set the house on fire to exact revenge on her neglectful parents.
To her surprise, Saya hears Yuu behind her, asking if she believes that she did it. Unable to respond, Yuu only smiles as she is taken away by an ambulance, causing Saya to chase after it to try and apologize. But before she gets far, Saya twists her ankle and falls over. The next day, Saya finds that Yuu hasn't come to school, leaving her to wonder what happened, wanting to apologize and make it up to her. Saya later finds Yuu near the river, just as Mato had when Yuu disappeared, and runs after her, grabbing her arm and apologizing as much as she can, stating she'll do whatever Yuu wants her to do to make it up to her if Yuu can forgive her.
After a brief monologue by Yuu, she turns to Saya, asking her if she is willing to do whatever she tells her to do. Saya replies "Yes." rather quickly to which Yuu states "Then protect me.". Saya seems confused as she is approached by Yuu, causing her to back up a few steps. Yuu grabs Saya's shoulders and brings their foreheads close together, much like she did for Mato. Yuu's eyes close before opening again, revealing them to be bright orange with the circular pattern much like STRength has, telling Saya to "Say your name.". Saya quickly replies with her real name, but Yuu states that she meant her "other" name. Still confused, Saya could only repeat what Yuu says before Yuu delves into her mind, finding her "other" self, saying "You are.... Black Gold Saw.".
With the flashback ending, iBRS breaks out of the hold of the pillars that kept her in place and proceeds to attack Black Gold Saw once again. Saya desperately tries to get Mato to come to her senses but fails as iBRS uses King Saw to try and land the finishing blow. Before she could, STRength saves Black Gold Saw by punching Insane Black Rock Shooter away, blasting the ground as STRength grabs BGS and escapes to the next world (Likely STRength's world) pursued by Black Rock Shooter. STRength hides BGS away in a stone box and Saya is again back in the real world stating, to her surprise, that the "other girl" saved her, despite the horrible things that she did. Yuu tries to comfort her, saying "It's okay.. She forgave you.". Saya then says that she doesn't understand and she had a duty to protect that world but couldn't do anything against Insane Black Rock Shooter and breaks down in tears as Yuu holds her, apologizing to her as well as Mato and Black Rock Shooter.
- She states to Mato that she actually hates coffee. Without milk, that is.