TOKYO—On a stormy night, three mysterious figures clamber onto an uninhabited island in the East China Sea. Tensions spiral upward from there until China invades several Japanese islands, triggering Tokyo’s first use of military force since World War II in a fierce battle on land, air and sea.

It is all fiction, laid out in a series of manga cartoon novels called “Aircraft Carrier Ibuki” that has sold more than three million copies in Japan by presenting a plausible tale of the nation’s military future. Coming next: a movie version and a real-life national defense plan, the first in five years, that could mandate some of the weapons seen until now only in the manga’s pages.

One question raised by “Ibuki” also lies at the heart of the defense review: Should Japan’s military be able to strike at other nations?

Tokyo’s aggression during World War II makes the acquisition of offensive military capabilities sensitive at home and in neighboring countries. Japan’s military was disbanded after the war before being reformed as the Self-Defense Forces and relegated to a role many Japanese see as primarily providing disaster relief.

Prime Minister Shinzo Abe has loosened some legal restrictions on the SDF but it remains tightly constrained on when it can engage in combat.