Having won the 63rd National Sensha-dou tournament, the girls from Ooarai High managed to prevent their school from closure by the Japanese Ministry of Education. However, new troubles loom on the horizon: a ministry official argues that the deal was not legally binding and that the Ooarai school carrier is to be decommissioned. Students and their families are frustrated with this injustice and overwhelmed with despair; it seems little can be done to save the school.

Their last glimmer of hope is a proposed match against the All-Stars University Sensha-dou team, consisting of the most talented students from all over the country. Despite Ooarai being severely outnumbered and clearly outclassed, they accept the challenge.

During the Taishou period of early 20th-century Japan, Haru Asagi is sent to work as a maid to support her struggling family. The Miyanomori family, which she serves, is highly influential across Japan and consists of one of the nation's top magnates and his six sons—but power and money have brought out the cruelest in these brothers. When the head of the family announces his retirement, the six Miyanomori brothers are left to vie for his position. With 18 years of experience separating the oldest and youngest brothers, frustration and competition are rife. As a result, Haru is left to deal with each of the vastly different siblings and explore the depths of their true selves. All the while, a greater conflict lies in wait with the potential to destroy everything their father has built for them.

In Japan, there exists a government agency known as the Supernatural Disaster Countermeasures Division (SDCD), whose duty is to protect the citizens from creatures unseen. They are able to dispatch these monsters swiftly and without alerting the general public. But currently, they face a different challenge: the betrayal of one of their own. After the death of her mother several years ago, Kagura Tsuchimiya has been fostered by the Isayama family and forms a close sister-like bond with their daughter Yomi. The two become inseparable, and together they work for the SDCD as highly skilled exorcists. However, as the stress and consequences of their sacred duty weigh on them both, and family politics come into play, Kagura and Yomi begin to slowly drift apart. One of them grows earnestly into her role as an exorcist, and the other heads down a dark path from which there may be no redemption...

One year ago, a UFO containing 150 aliens crash-landed off the shores of Kasai. Because no one could fix their ship, the Japanese Government decided to bestow upon them the designation "DearS" and make them into Japanese citizens, teaching them the language, customs, and culture of Japan. However, in order for them to become more familiar with human society, a home-stay program has been enacted to allow them to mingle with other humans. One misty morning, a truck carrying a capsule that housed one of these aliens ends up dropping it into the riverbank, releasing her from her confinement. She is eventually found by a high school student named Takeya Ikuhara, who saves her from being hit by a truck and takes pity on her, despite being extremely distrustful of their race and wanting nothing to do with them. Upon being named Ren, she imprints upon him as her "Master" and serves as his personal "Slave," leaving him with a "DearS" who wants to remain with him no matter what and bringing his ordinary, alien-free days to an end.