It's interesting to see how countries are reinterpreting laws to 'expand' the legal boundaries of conflict. Essentially, Japan now interprets 'self-defense' to no longer just mean defending the country when under attack, but to also include assisting allies in foreign countries. This sort of the same legal basis most countries are using to bomb targets in Syria (and Japan will probably use it too) - Iraq has asked the US and it's allies to help them defend themselves against ISIS, and bombing Syria to defeat ISIS counts as defending Iraq.