There’s a long road ahead to get there, but nothing like a potential nuke warhead shooting overhead to overcome decades of mistrust.

Missile games in Asia

Michael Auslin

Pyongyang already shot a two-stage Taepodong missile directly over Japan’s main island, Honshu, back in August 1998. Japan has had success in shooting down test missiles in the ascent and mid-course stages of flight, using their sea-based SM-3 missile fired off of Aegis-equipped destroyers (of which the Japan Maritime Self-Defense Force has four ships). And Japan and the U.S. are jointly developing an upgraded version of the SM-3. 

http://www.aei.org/article/foreign-and-defense-policy/regional/asia/missile-games-in-asia/