The basic plot is that an orphan girl named Midori is taken in (read: enslaved) by a traveling freak show. The freak show includes such unsavory characters as a mummyman, a snake woman, and a drooling man with no limbs. The owner of the freak show, the eponymous Mr. Arashi, is a strict man who allows his freaks very little freedom or joy in life. He is especially cruel to Midori, our heroine. Midori works, not as a freak since she is normal, but as a sort of caretaker of the freaks. (Source: everything2)

Volume 1 : The Laughing Vampire.
While a young boy, just resurrected as a vampire, commits acts of awful ferocity, the city around him shows all its perversion. The adults abuse of their power, the boys degenerate and use all the available means to achieve their goal to give vent to their low instincts. Whoever can't understand and make opposition is doomed to change or becoming crazy. So which is the real horror? The vampire who kills in order to feed himself or the crawling disease hidden in the society that slowly corrupts without being noticed?

Volume 2 : Paradise.
Following the events narrated in the first volume, Luna and Konosuke are now living together with the old woman vampire as fellows, as lovers, in a diabolic innocence, killing to quench their thirst for blood, joining death and love under the dream of the eternal youth. Meanwhile a young boy, named Makoto, is looking for his lost sister Miko, who disappeared years ago under mysterious circumstances. But what has really happened to that girl who liked eating grubs and dreamed to become on of them? And is someone really hiding a terrible secret? The paths of all the characters will dramatically collide, bringing unexpected consequences after the things are gradually revealed.

A story suspended between weirdness and decadence, showing a clear nostalgia for the German cinematography and Federico Fellini, where the blood is used to trace a great and only apparent amoral story.

1-2. Binzume no Jigoku (The Inferno in Bottles)
3. Sei Anthony no Yuukai (The Temptation of Saint Anthony)
4-5. Koganemochi
6-7. Kawaisou na Ane (Poor Big Sister)

The manga centers on a set of twins with an older brother and younger sister. The twins were born with a set of odd matching birthmarks on their sides. After their mother abandoned them their stepfather sold them off to a freak show. The story tells what becomes of the twins afterward.

(Source: ANN)

Gichi Gichi kid is a full manga about a boy with magical powers. The same adventures of children with the unique Maruo′s vision and elegant drawings; this kid is always making good for the people; nothing to do with the autor usual works.

This volume consists of the one shot stories:

Putrid Night (1981)
Sewer Boy (1981)
A Season in Hell (1981)
Shit Soup (1982)
The Great Masturbator (1982)
Putrid Night: Raven of Oedipus (1982)
Sewer Boy: Paradise (1982)
Voyeur in the Attic (1992)
Non-Resistance City (1993)

It's about a boy with mysterious powers who transfers from school to school, fighting various monsters.

(Source MU)

Collection of short stories by Maruo.

It's almost impossible to summarize them, most of them aren't really plot driven but they deal with abnormal states of the mind and are permeated by a general surrealism.

As in many of this works, he shows references to the art and culture of 1920s and 1930s Japan and Germany which had inspired his own artistic style.