Yakeppachi no Maria

This is a bizarre sex education Manga staged in a school, featuring a rowdy boy called Yakeppachi and a girl named Maria, who is the ectoplasm of Yakeppachi. Yakeno Yahachi, a rowdy boy known as "Yakeppachi" gives rise to a pretty girl named Maria while in a trance, and her personality is identical to Yakeppachi. Actually, she is the "ectoplasm" of Yakeppachi. "Ectoplasm" is a hazy stringy and fog-like substance that is generated from the spirit medium at a seance, also referred to as an "astral body." Taking on the form of a doll given to her by Yakeppachi's father, the ectoplasm Maria begins to go to school with Yakeppachi.

The whole school is thrown into a state of confusion except the classroom teacher Akita, who is the only person to understand that this is a supernatural phenomenon. The plot thickens when, after finding out about the secret of Maria, a juvenile gang group ("Group of Tateyoko") that has been keeping an eye on Yakeppachi, start to follow him, thinking to stage an attack. Another enemy of the pair is Yukisugi Midori, girl leader of the "Group of Tateyoko," who is offended by the fact that Maria is popular with the boys, and tries to attack with the intent to hurt her...

(Source: Tezukaosamu.net)