I think this can be interpreted in showing how important the US Army considers missile defense for Japan that it stood up a brigade headquarters there:

Col. Patrick Costello speaks after taking command of the newly reformed 38th Air Defense Artillery Brigade at Camp Zama, Japan, Wednesday, Oct. 31, 2018.

The Army has reactivated a brigade to oversee missile-defense units on mainland Japan, Okinawa and Guam.

The 38th Air Defense Artillery Brigade was reactivated in a brief ceremony Wednesday at Camp Zama, headquarters of U.S. Army Japan in Kanagawa prefecture near Tokyo.

The brigade, based at Sagami General Depot, about 25 miles west of the Japanese capital, will oversee the 1st Battalion, 1st Air Defense Regiment at Kadena Air Base, Okinawa, as well as the 10th and 14th Missile Defense Batteries on mainland Japan and a Terminal High Altitude Area Defense, or THAAD, battery on Guam.

The unit, which will include about 115 personnel at full strength, is purely a headquarters unit, said U.S. Army Japan spokesman Kevin Krejcarek.

“It’s just personnel. There won’t be any missile batteries at Sagami,” he told Stars and Stripes ahead of Wednesday’s ceremony as protestors gathered outside Zama’s main gate.  [Stars & Stripes]

You can read more at the link, but for those wondering USFK has its own air defense artillery brigade headquarters based at Osan Airbase.