It looks like Japan is thinking of introducing their own THAAD system as well:

Japan’s Kyodo news agency reports the government may be following in South Korea’s footsteps on deploying U.S.-provided THAAD missile defense.

Kyodo says Tokyo will soon set up a THAAD review committee to examine the system in detail.

Japanese Defense Minister Tomomi Inada visited a THAAD unit on Guam Friday and was briefed by U.S. officials.

She says there’s no concrete plan to introduce THAAD quite yet, but warns that North Korea’s missile and nuclear development has entered what she calls a new phase.  [KBS World Radio]