On the surface, Koudo Ikusei Senior High School is a utopia. The students enjoy an unparalleled amount of freedom, and it is ranked highly in Japan. However, the reality is less than ideal. Four classes, A through D, are ranked in order of merit, and only the top classes receive favorable treatment. Kiyotaka Ayanokouji is a student of Class D, where the school dumps its worst. There he meets the unsociable Suzune Horikita, who believes she was placed in Class D by mistake and desires to climb all the way to Class A, and the seemingly amicable class idol Kikyou Kushida, whose aim is to make as many friends as possible. While class membership is permanent, class rankings are not; students in lower ranked classes can rise in rankings if they score better than those in the top ones. Additionally, in Class D, there are no bars on what methods can be used to get ahead. In this cutthroat school, can they prevail against the odds and reach the top?

​Like many in her class, Koyuki Honda looks forward to her graduation ceremony. However, while her peers have family to attend, Koyuki has no one, as her only family—her brother—died years ago. While visiting his grave, she meets two brothers named Kiri and Victor Putin chasing a strange creature. They try to assure her that they are just actors shooting a movie; Victor, however, piques Koyuki's curiosity about the old legend of the clock tower at the cemetery: if you make a wish under the clock tower at midnight during a full moon, time will turn back, allowing someone to reclaim what they have lost. Deciding to make her wish, Koyuki learns the horrifying truth: the legend is a ruse for time demons called "Horologues" to steal humans' time. As they are drawn to regrets, Victor uses Koyuki as bait to lure a demon there. Kiri and Victor explain that they are Chronos Rulers, warriors who fight against the Horologues using the "Oath of Time"—an item allowing them to speed up or slow down time. With the demon destroyed and the crisis averted, Koyuki is able to go on her way free from regrets. However, she is not the only human with sorrows. The two boys must continue to hunt down Horologues in order to keep humanity safe. [Written by MAL Rewrite]

On his high school graduation day, Itsuki's cousin, Mahiru, tells him that she's pregnant. Just then, a gate of light emerges and transports the two into the world of Granvania. In this land, "Impurities" have been causing a disturbance to the Stars, ultimately plunging Granvania into chaos and disorder. And Itsuki, now revealed to be one who is fated to meet with the "Star Maidens," is seen as Granvania's last hope and was thus given the task to produce "Star Children" and combat the "impurities." And unless the task is complete, Itsuki may never be able to return home. (Source: Wikipedia, edited)

Legend tells that when the Earth was destroyed, the great clockmaker Y made a replacement from cogs and gears. Naoto Miura is a young boy who aspires to be a great clockmaker. However, despite his unique talent—sensitive hearing that can immediately understand clockwork mechanics from noise alone—he has made little progress. But this changes when a coffin falls from the sky into his apartment, revealing RyuZU, a female automaton forged by Y himself. News of RyuZU's arrival brings Marie Bell Breguet, the gifted heir of a distinguished line of clockmakers, and her cyborg bodyguard Vainney Halter into Naoto's life as well. When she and Naoto both become embroiled in an action-packed battle for their lives, they discover an uncomfortable truth: the clockwork planet that humanity has lived on for over a millennium is beginning to break down—a secret that many people will kill to protect. [Written by MAL Rewrite]