Eight words describe the feelings of Youtarou Hanabusa: "I just want to live a normal life." Unfortunately for him, as a member of the Knights of the World, his training in this ancient and international order has left him with a condition he calls "White Knight Syndrome." This condition causes Youtarou to instinctively act heroically and chivalrously whenever he encounters someone in danger. To protect his identity in such embarrassing moments, he carries a mask with him at all times. Then one day, he saves the life of Makio Kidouin, the young daughter of an elite and affluent family. Little does he know that this singular act of heroism will change his life forever. Soon, he is simultaneously blessed with a life in the lap of luxury and cursed with one of abnormality, for his new friend Makio lives a life far removed from the everyday. Between coping with the hijinks of six-year-old Makio, and dealing with a cast of odd friends and scheming enemies, Youtarou must protect his new friend while keeping his identity hidden as the masked hero Knight Lancer.

Onboard a cruise ship heading to the scenic Cenancle Island, the full-body cyborg Nene Nanakorobi, a bubbly young girl who dreams of world peace, meets inventor Uzal Delilah. The two become fast friends along with Uzal's pet cyborg Clarion, a cat-like combat android. Soon after parting ways, a terrorist attack on the island threatens to shatter the pair's new friendship. In a bid to save her new friend, Uzal gives Nene the ability to use the Pandora Device found in Clarion's body before seemingly dying. With this power, Nene can temporarily master abilities and skills never seen before in the advancing world. Working together, the two unlikely companions go on various missions—from saving children in shopping mall fires to fighting reckless thieves—all in the name of world peace. But to achieve this goal is not easy. B.U.E.R, a sentient laser in the form of a misshapen teddy bear, threatens to wreck their happy lives with his perverted nature and uncontrollable power. And to make matters worse, Nene's guardian, as well as genius inventor, Takumi Korobase has an undying interest in B.U.E.R. Burdened with saving the world and keeping B.U.E.R from the hands of evil, Nene and Clarion's desire for world peace seems like a pipe dream. With this monumental goal, could the weight of it all destroy the pair's friendship completely?

For high school students like Shouichi Kamita, university entrance exams and the future are common concerns. It is also during this time in life that a mysterious emotion that vexes people of all ages may begin to weigh upon one's mind—love. At this point in his teenage years, Shouichi finds three girls he could see himself having a future with: the ever-cheerful Hikari Tsuneki, who teases Shouichi without mercy, but actually has a softer side; the competitive gamer, Tooru Miyamae, who has difficulty communicating with others; and Shouichi's childhood friend, Kyouko Touno, the sometimes immature shoujo manga enthusiast. Seiren follows Shouichi's relationships with these three girls across three separate arcs, as their feelings grow from mutual interest and blossom into something more beautiful.

Three girls have been chosen by the great Shinju-sama to be heroes and fight against the destructive beings known as Vertexes—enemies that threaten the harmony and safety of the world. Unsure of when they would be called to duty, Sumi Washio, Sonoko Nogi, and Gin Minowa spent their time idly. However, with the sudden appearance of a Vertex, they realize they have no idea how to fight together as magical girls when they are nearly bested. They manage to defeat their enemy by sheer determination, but in the aftermath of the battle, the three decide to fix their teamwork issues and improve their combat capabilities. But as more enemies appear—and requiring even more power to defeat their nemeses—the girls may find themselves irreversibly changed by the use of their magic. What price will they have to pay to ensure victory, and is it one worth paying if humanity will be saved?