Sayo is a petite girl with an average height. She has shoulder-length, dark, red hair. She has tattoos on her body to seal her immense power.
After the timeskip, Sayo has gotten taller and has taken to wearing the standard exorcist gear when on missions.
She is very caring towards others and acts flirty around Rokuro. Due to being a child, she is able to openly show her affections whereas the other girls who have crushes on him are unable to show it.
She even offers to give her own life for others such as when she was kidnapped. Since she was confined in her house for most of her life, she shows interest in the outside world.
Upon arrival, she sneaks into a sleeping Rokuro's bed and he wakes up running out of his room to meet Benio and Mayura (who walked in on a naked Shimon). When Benio and Mayura see Sayo, they seize Rokuro by the neck and his face thinking he did something to her but Sayo saved him and admonish the two for their treatment towards him, to their shock. Shimon introduces Sayo to the others and tells them of her status as the test proctor and cousin. Sayo makes Rokuro go shopping with her. They are observed by a jealous Mayura and Benio who see that Rokuro was right about her flirtations but soon learn hardships from the accompanying Shimon and how she sees Rokuro as a savior for indirectly saving her.
When one of Sayo's flirtations go too far, Benio steps in and Sayo insults her by bringing up her proud lineage compared to Benio's which contains her traitorous brother Yuto Ijika. This causes Rokuro to get angry and harshly reprimand her for her words as Shimon appears and tells Sayo she deserved that as she runs off in tears. Sayo runs to the park where she cries thinking Rokuro hates her before Benio appears and Sayo apologizes as Sayo asks how she feels about Rokuro and sees the latter has feelings for him as well before stating she has to be more open to him as she couldn't lose to her. Rokuro arrives questioning the mood as Sayo decides to begin their test that night, much to their excitement. Afterwards, she unleashes Kuzunoha and brings out Rokuro's guardian, which causes all Sayo's guardians to bow down. She is rendered unconscious as a result of her usage of her power and Shimon carries her to bed so she could recuperate. Upon awakening, she sneaks back into an unconscious Rokuro's room holding him before falling asleep. Rokuro awakens and tells her to stop that habit as Benio arrives an admonishes Sayo for it as well. Sayo then gives her judgment calling it a "shame" as he was destined for endless battles as she deems him worthy of going to Tsuchimikado Island.
She gets abducted and is severely injured by the Basara. She unleashes Kuzunoha in Magano to summon Benio Adashino's guardian spirit, which turns out to be Kuzunoha's enemy, Ashiya Doman. However, she is rescued by the latter and leaves the mainland stating that she would wait for Rokuro.
In Chapter 79, she makes a long awaited appearance, kidnapping Rokuro and confining him to a chair with a rope. Later, as the group is headed to the Gate, she comes dressed in red Ikaruga hunting gear. During the mission, Sayo challenges Benio to a kegare exorcising race, and her true power is shown in the form of a fox. The race ends in a tie, and as Sayo is overcome with a curse that amplifies the emotions, she declares she wants to be rid of everyone. Adashino snaps her out of it, and she sadly congratulates her on their engagement. The four of them regroups, and they finish the kegare off together.
Powers and Abilities
Her guardian spirits are Kuzunoha, the mother of Abe no Seimei, and her 48 retainers. To use her power she has to be naked and perform a kegare ritual. Sayo also has the ability to wield a large amount of spiritual power in battle, with a fox-shaped aura.
Sayo is the younger cousin of Shimon Ikaruga. He is extremely protective of her, and often tries to keep her from using her immense power too much. Shimon often calls her Chiyo, having misread her name at an early age. She often refers herself as his "sister", even though he is from a junior branch. In one of the arcs, where Sayo and Rokuro were out touring the cities, and Sayo backtalked Benio, Shimon did not hesitate to put her back in her place, saying that she is tarnishing the family name. In the later chapters, he also said he did not expect her to go into battle in only three years' time.
She is the younger sister of Keiji. They get along well and he is protective of her as Shimon.
She has a huge crush on Rokuro seeing him as her "prince charming who rescued her from the tower," due to being confined in her household under exorcists' law of protection. Sayo snuck into his bed while he was sleeping twice. When visiting the Ikaruga House, Sayo immediately invites Rokuro to her bedroom, though he declines.
Even as a teenager, Sayo still has interest in Rokuro and tried to halt his engagement with Benio. Rokuro was annoyed by her repeated advances but amazed at her being an Exorcist. After a mission, Sayo accepts that she can’t take him and begrudgingly accepts his standing with Benio. 
Sayo became friends with him after seeing he was having a hard time with his occupation. Sayo tried to get him to take a break, since they are the same age. At first, he tried to ignore her but she insisted that he go in for some to spend time with her and their friends. Arimori ended up having fun and thanked Sayo, who blushed in gratitude.
- The name Sayo means "small" (小) (sa) and "night" (夜) (yo).
- During the mid-credits scene in the final episode of the anime, Sayo is briefly shown sleeping.