I think the Japanese could kick China's a$$ if they wanted to. They are technically pacifist, but could become a nuclear power with the flip of a switch. Of course, if it goes nuclear all bets are off, but neither side is that foolish.
Living here the past 25 years and a retiree, I'd say Japan's defense is as big as the USA's military umbrella.
Remember, Monster Island is just off shore. If they turn off the lazer fence, look out.
Gamara, Godzilla, Rhodan....