As East Asia is entering the 21st Century, Japan, in reassessing its security environment and thus its strategic calculus, is on the verge of deploying latest jointly-researched theater missile defenses (TMD) to counter the threat of ballistic and cruise missiles. In parallel, the People's Republic of China is constantly modernizing its ballistic missile forces and is gearing up for a possible contingency with its self-proclaimed "high-tech adversaries". This work shows what drives Japan to deploy theater missile defenses and how the People's Republic of China is poised to be reacting to it.