In an underground world where tunnels extend everywhere, even though they live in dark and confined spaces, people wear protective clothes and lead quiet and enjoyable lives. Patema, a princess in her underground village, loves to explore the tunnels. Her favorite place is a “danger zone” that her village prohibits people from entering. Even though she’s scolded, Patema’s curiosity can’t be held back. No one ever explained what the supposed danger was. On her usual trip to the “danger zone,” Patema faces unexpected events. When hidden secrets come to light, the story begins to unfold.

Every person has his or her own little world. Among the 34 bustling students of classroom 2-1, there are many such worlds. Honjou Akio’s world—my world—is filled with passionate talk about last night’s anime with Yoshida, Watanabe, and other friends. It’s an fun, comfortable place… But, I always wonder. Wonder about the world of Makina Juri, smiling and surrounded by gorgeous friends on the other side of the classroom. One day, I enter her world. But it’s not as simple as it sounds.