The anime feature (AKA ) opens with an alternate ending to World War II, when the islands of Japan are divided into northern and southern territories, and the island of Hokkaido - Japan's second largest prefecture, at the nexus of the Sea of Japan, the Sea of Okhotsk and the Pacific Ocean - is annexed. Around the turn of the millennium, an enigmatic tower is constructed on Hokkaido, and though its purpose is inscrutable to the locals, it causes the tension between the northern and southern territories to double in intensity. As this occurs, two local teenage boys - friends since early childhood - contemplate the mystery of the tower and devise plans to build a plane that will enable them to explore it. They also fall hopelessly in love with the same girl, who lavishes her attentions on each. The three vow to always stay together, and to see the plans for the airplane through to fruition, but in time the friends forge separate paths and a devastating sickness threatens to claim the girl's life. What they cannot even begin to anticipate are the truths that will be uncovered when time and destiny pull them back together.