Ai Onbara and his friends used to be inseparable. They had it all: special nicknames for each other, a secret base up in the mountains, and even their own secret society dedicated to safeguarding the world (or conquering it, depending on who you asked). With their intrepid leader Hiiro at the helm, everyone believed that their team, the Defense Force, would last forever.

But then Hiiro moved away. Ai was left to take her place as the group’s leader, and in no time at all, the Force fell to pieces. With their friendships fractured, its members were left to gradually drift apart. It seemed they would remain estranged forever… until one day, out of the blue, Hiiro returns! She’s ready to pick up right where she left off, and much to Ai’s chagrin, she has no intention of taking no for an answer.

The chime of a bell rings out, and with it, the return of the Defense Force is set into motion…