As Tokyo spins up its defense industry for the country's largest military expansion since World War II, it has run into a challenge: Some of Japan's best-known brands are reluctant to invest in the military side of their businesses.

Japan, which renounced war in 1947, last year unveiled a five-year $315 billion military expansion to deter Beijing from using force in the East China Sea amid growing concern that Russia's attack on Ukraine could embolden China to invade Taiwan.

But a key part of Tokyo's strategy hinges on persuading commercial firms such as Toshiba, Mitsubishi Electric and Daikin Industries, which for decades have quietly armed the country's Self Defense Forces (SDF), to ramp up production.