After the events of the 2nd season, Ai's three helpers, Ichimoku Ren, Wanyuudou and Hone-Onna live out their lives in relative peace. This is suddenly shattered when Kikuri returns to recruit them. Meanwhile, Ai mysteriously reappears from the dead and uses the body of a young schoolgirl, Yuzuki Mikage, to continue the Jigoku Tsūshin operation. Yuzuki is aware of Ai's presence however, when she can see what Ai sees.
— Description from AniList community (anilist.co).
