The tragic killing of the two hostages reinforced domestic concerns over Japanese rearmament. If they want to reinforce their (recent) pacifist heritage, so be it. But they should not then expect Washington to protect them. Serious countries defend themselves. They don't turn their futures over to other nations to save a little money.
Just in case anyone was in doubt of his intentions, Shinzo Abe made a high-profile visit to Yasukuni Shrine in December, the first time for a Japanese prime minister in seven years. The real reason for Abe's visit, which elicited predictable outrage from Korea and China, was that he felt that he could get away with it.