Sasa is a yōkai who was previously trapped in a small rear shrine and forcefully made to disappear by Sakae.
Sasa is a large one-eyed spider.
After Haruitsuki and Hanae tells a yōkai called Bonta that they'll exorcise him another day, Sasa leaves however Haruitsuki notices another presence of a yōkai other than Bonta but moves on thinking it was just his imagination. That night Sasa possesses Bonta and uses Bonta as bait for the two.
Next day Hanae and Haruitsuki tries to go find Bonta and follow up till they find stairs, Haruitsuki finds this suspicious as he can sense the presence of more than one yōkai (other than Bonta and Fuzzy), Hanae decides that he will go up first while Haruitsuki waits at the bottom so in case they find 2 demons to exorcise, opening two portals would tire Haruitsuki out. A old lady called Yamaoka approaches Haruitsuki. Haruitsuki tells her that his companion is up the stairs but the old lady tells him that there's no stairs there and warns him that something may be drawing them in and there would be no returning back.
Haruitsuki climbs up the stairs and notices the entrance fades away, Fuzzy clings onto Haruitsuki's face and Hanae (holding Bonta) tells him that no matter how many times he tries to descend down the stairs, there are still another never-ending set of stairs to descend. Haruitsuki inspects Bonta and says that he's been possessed, Ashiya then asks if maybe that demon's possession is a link to what's going on with the stairs, Haruitsuki agrees and decides to summon the Mononokean. Unfortunately the Mononokean doesn't come and he says that their only choice is to go further up.
They reach to the end of the staircase and in front of them is a sealed shrine, Sasa tries to tell them a lie to lure them further to open the door, Haruitsuki explains his position and tells Sasa that he cannot exorcise it since he cannot trust Sasa who is preventing the two from leaving the shrine. Unhappy with this Sasa attempts to possess Haruitsuki however he was quick enough to catch it before it could with his influence, Sasa then tells him that instead it could just possess Hanae since he's easier and succeeds.
While Sasa controls Hanae's mind, Fuzzy and Haruitsuki attempt to get Hanae out of Sasa's control. However with the assistance of a possessed Bonta, Haruitsuki is pinned down on the ground by Hanae's hands grasping his neck. After Haruitsuki slaps him Hanae begins to gain his senses for a moment. Seeing Haruitsuki on the ground and not moving, Hanae panics, thinking that he killed him. He hears a mutter of a unfamiliar voice telling him that he will die at this rate and sees someone who looks like Haruitsuki followed by losing his consciousness.
Sasa then orders Hanae to open the door. Haruitsuki gets angry and tries to get Hanae off him. Sasa is clearly annoyed that he was still alive and orders Hanae to kill Haruitsuki. However, Hanae tells Sasa to shut up and goes over to open the door. Hanae asks why Sasa wasn't leaving and Sasa who was frightened asks why Hanae had golden eyes, Hanae responds that he is not an ordinary human and exorcises Sasa by commanding it to disappear using his influence.
Before Sasa disappears, Haruitsuki gets a glimpse of Sasa's memories; a blonde high school student about to exorcise Sasa in the past and decides to see if he can seal it in which he succeeds.
- Sasa was the first yōkai to get sealed by Sakae.
- Sasa has the ability to possess￼ a human and a yōkai simultaneously.
- When he succeeds in possessing a yōkai or a human, the victim's eyes have the outline of a cobweb formed in the iris.
- ￼According to Sakae, Sasa previously used to lure and trick humans to release him.