Ayumu Narumi has lived all his life in the shadow of his famous detective brother, Kiyotaka. However, Kiyotaka disappeared two years ago, leaving behind his wife Madoka and Ayumu himself, along with a cryptic message about the Blade Children. One day, a girl at Ayumu's school suddenly dies. What seemed like a suicide at first glance turns out to be a murder, and Ayumu is the prime suspect. While investigating the person responsible for framing him, he discovers that the mysterious Blade Children are involved—and they somehow know Kiyotaka personally. Ayumu soon finds out just how dangerous the Blade Children are and learns that, in reality, he and Kiyotaka are intertwined more closely than he had ever believed.

Formerly an all-boys school, Seigetsu Academy is now a co-ed institution that hones its students' knowledge in astronomy. In this regard, Tsukiko Yahisa enrolls as the first and only female student in the academy. By her side are her childhood best friends, Kanata Nanami and Suzuya Touzuki, who shield her from the advances of the student body. As Tsukiko learns to navigate her new environment, she encounters 13 distinct boys who are based on the Western zodiac star signs. Eventually, Tsukiko's involvement with these boys drags her deeper into star-crossed routes that will entangle her in numerous affairs.

Shiina Aki is constantly being treated like a girl due to his feminine looks so he decides to move to Tokyo to attend middle school in an attempt to change himself. However, what awaits him in his new home, Sunohara-sou, is the kind-hearted caretaker, Sunohara Ayaka. Along with the three female members of Aki's new middle school's student council, Yukimoto Yuzu, Yamanashi Sumire, and Kazami Yuri. And so begins Aki's new life in Tokyo living with four girls.

It is two hundred years after the beginning of the Space Era, when human civilization on Earth began expanding into space. However, by the start of the 21st century, two meteors struck the planet, sending humanity into chaos. By the year 179 of the Space Era, secret technology, dubbed Extra-Over Technology, or EOT, was discovered by the Earth Federal Government within a third meteor that hit Earth in the Marquesas Islands of the South Pacific. Dr. Bian Zoldark, head of the EOTI Institute (Extra-Over Technological Investigative Institute), had evidence the creators of the EOT were heading to Earth, in order to reclaim it...or worse, invade the planet. In order to defend humanity from extraterrestrial threats, the government begins to research and develop humanoid mecha called Personal Troopers. (Source: ANN)