|The Hell Professor vs Hell Girl|
|Kanji Title||地獄博士 対 地獄少女|
|Romaji Title||Jigoku Hakase Tai Jigoku Shoujo|
|Original Air Date||February 21, 2009|
|Snow, Moon, and Cherry Blossoms||Right in Front Behind You|
"The Hell Professor vs Hell Girl" is the 20th episode of the season "Three Vessels" and the 72nd episode from total.
After awaking in Tsugumi’s health office, Yuzuki asks what Tsugumi knows about Ai Enma but Tsugumi refuses to give Yuzuki a clear answer. Later, Yamawaro and Kikuri approach a large mansion belonging to a client but are unable to enter due to an encircling barrier. At night, the owner of that mansion, Shogo Mizorogi, accesses the Hell Link website and types Tsugumi's name in. Each sensing the request, Yuzuki, Ai, and Tsugumi make their ways towards the mansion. Once they gather, he explains that he initially gained interest in Hell after his mother used Ai's services to send his father to Hell. After a great deal of research on Hell, he eventually yearned to meet Ai. Learning that she had once more regained her body, he nurtured a grudge against Tsugumi through hypnosis in order to meet her. Ai agrees to give him Ichimokuren as a doll, however just before Shogo can completely pull off the string, he is instead sent to Hell by his assistant Kikyo using Yamawaro; he is exacting the grudge that the many children bore whom Shogo treated cruelly for the sake of his research.
- The episode marks the first appearance of Ai's Grandmother in Three Vessels.