Advanced placement into a school of higher grade proof-reading is determined by the results of the Promotion Test strictly for class type. Ranging from A class with the best facilities anyone can offer all the way down to F Class which is composed of low dining tables, rotten tatami mats and other worn out facilities. Students can change classes by competing using the Examination Summons Battle system or ESB. Students summon characters with their equivalent test mark scores and use them to compete with other classes.

Oreimo follows the daily life of an ordinary high school boy named Kyousuke Kousaka. Kyousuke’s younger sister Kirino is a pretty fashion model, but also hides a dark secret of being an otaku of adult games. Kyousuke is the only person to whom Kirino reveals her hidden obsession and other issues.

16-year-old Hayate is really down on his luck. Because his unemployed parents are good-for-nothings who waste what money they have on gambling, Hayate had to start working at a young age to help out his family. Although such experience has made him inhumanly fast and tough and skilled at things boys aren't normally skilled at, it has also left him in an awkward position, as his parents have racked up such a huge gambling debt that they have sold Hayate to the yakuza for the value of his organs. In a desperate attempt to avoid that fate, Hayate decides to become a "bad guy" and kidnap someone to be held for ransom, but his efforts to do so are mistaken as a confession of love by the girl he targets. When he helps save the (as it turns out) ultra-wealthy 13-year-old Nagi from real kidnappers, she takes him in and gives him a job as her new personal butler (and love interest) until he can pay off his debt. But Hayate is more attracted to Nagi's beautiful teenage maid Maria, and head butler Klaus is initially disapproving of a boy with such a poor look. And then there's Nagi's pet Tama, who is also a force to be reckoned with.

The students of Class 3-E have a mission: kill their teacher before graduation. He has already destroyed the moon, and has promised to destroy the Earth if he can not be killed within a year. But how can this class of misfits kill a tentacled monster, capable of reaching Mach 20 speed, who may be the best teacher any of them have ever had?

For 30 years, thousands have traveled to other worlds. The few that return keep the powers they had in those worlds. Akatsuki Ousawa returns from the world of Alayzard with the defeated Demon King's daughter, Miu. Miu pretends to be Akatsuki's sister to hide her true identity. They join Babel, a school for inter-dimensional travelers, and struggle against the student council to uncover the truth behind the school.

One rainy night after a school festival, a group of students from Kisaragi Academy decide to perform the "Sachiko Ever After" charm, which will unite them forever as friends. Once the ritual is done, a sudden earthquake transports them to Heavenly Host, a torn down elementary school. Unbeknownst to Satoshi and his friends, however, is the horrific past behind it which culminated in its demolition. As they look for each other and try to escape from Heavenly Host, they soon find out their lives are at the mercy of those affected by that same bloodied past.