Takao Kasuga is a lonely boy who spends his days immersed in books to escape his frustration with life. His only source of joy is the beautiful Saeki, who he secretly admires from afar. However, Takao's obsession goes too far one day when, in a moment of emotional folly, he steals the girl's gym clothes and takes them home with him. Worse, his terrible deed is spotted by Sawa Nakamura, a mysterious outcast who sits behind him in class who threatens to reveal the boy's secret unless he promises to engage in a contract with her. At first it seems Sawa just wants some companionship, but soon it becomes clear that this "contract" involves more than mere afternoon chats. In fact, Takao is about to discover just how dangerous his bond with Sawa is and how it threatens to tear everything - his life, his love, and even his sanity - apart.
Hideo Aiba is anything but popular. Not only is he a high school virgin, he's also a part of the "Roman Club" – a group of guys with bizarre fetishes. But Hideo's unusual school life is changed forever when the mysterious Kurumi transfers into his class, joining the Roman Cub soon thereafter. Together, the two begin a strained and pleasurable relationship where Kurumi controls Hideo's very desires... and actions.
Sundome is hyper-ecchi, unlike The Flowers of Evil, but both series are about a dweeby teenage guy who ends up in a twisted, S&M relationship with a sadistic female classmate. If you liked the femdom, or dark psychological themes of one of these titles, check out the other.
The relationships the protagonists share in these two stories are similar. However, while the relationship between the two in Sundome is sexually and psychologically exausting, the relationship in Aku no hana is simply psychologically exausting ( but it is not simple by all means)
Teenage genius Hiyama is fed up with the world: daily life is boring, and everyone around him is little more than living filth. One day, after a particularly trying day of tolerating the human scum that populates his high school, the boy decides that the only logical solution is to completely destroy the world and all of its useless creatures, then rebuild it as he sees fit. To this end, the teenager starts dabbling in hypnotism, and in a matter of months has half the school and even part of society under his control! However, this violation of free will won’t go unchallenged: another highly skilled hypnotist is determined to outsmart and stop Hiyama. In this dangerous game of cat and mouse, which man has the intellect to outwit and outmaneuver the other?
Admittedly, the plots of these two manga are nothing alike. However, if you really like main characters that think everone around them is repulsive/human filth/shitbugs, either may be up your alley. Also, both manga explore dark psychology, though Lost+Brain kind of flounders in this area.
Every day after school, the quiet and introverted student Kurosawa goes into the empty girls bathroom and "relieves himself". Besides this extremely odd ritual, Kurosawa also has a thirst for justice and a judgmental attitude towards his classmates. Upon seeing the bullying of an awkward girl in his class by two of the "popular" girls, he decides to bring justice to the bullies the only way he knows how. His plan for revenge goes "just as planned" until met by an unsuspected accomplice.
In both manga, our teenage protagonist is caught doing something pervy/embarassing (stealing a girl's gym clothes, etc.) by a female classmate, who lords it over him, and blackmails him into doing whatever she wants- or else she'll tell everyone his secret. Both are psychologically dark, but while Onani Master is also fairly uplifting, it's unlikely that The Flowers of Evil will be anything but twisted.