Two boys in Matsuyama spend their days hunting for the city's legendary seven wonders, treating it like a game that connects them to the place they call home. When mysterious strangers arrive in town with their own agenda, what starts as innocent curiosity becomes something far more complicated. Moburi, a high school girl who watches over the boys like an older sister, finds herself pulled into their world just as the real stakes become clear. Someone wants those seven gems badly enough to turn the city upside down. The boys must decide what matters more: the thrill of discovery or protecting Matsuyama itself. As trouble mounts and the truth behind the flying castle emerges, the trio learns that some secrets are buried for a reason. Their choices now will reshape not just their adventure, but the future of everyone around them. What starts as youthful exploration becomes a test of where loyalty truly lies.