Stocks

[Kyoto]-September's anti-Japanese protests in China over the disputed Senkaku/Daioyu Islands may have come and gone in the Western press, but the real damage is only just beginning for investors who have piled into Japan in recent years.

With their focus on the U.S. fiscal cliff and ongoing EU banking problems, many investors just don't understand how interlinked trade between China and Japan has become, nor the breadth of the damage this strained relationship can do to their portfolios.

But they're about to.

The breaking news here in Japan is that Honda cut its full-year net profit forecast by 20% following a 40% drop in September sales. That marked a 16-month low in sales that is directly related to nationalistic friction between the two nations.

That's adds up to a 95 billion Yen hit. To put this into perspective, Honda's net profit last year was only 211.4 billion Yen, so we're talking about a nearly 50% drop in the company's bottom line.

Under the circumstances, I would be very surprised if Nissan and Toyota, both of which also have significant operations in China, don't follow with similar results when they report next week. While I haven't seen estimates from Nissan yet, Forbes reports that Toyota sales are off a staggering 49% over the same time frame.

That's the biggest drop in a decade.

That's not inconsequential considering that Chinese-Japanese trade accounted for more than $340 billion USD in 2011. Japan is China's fourth-largest trading partner after the EU, the U.S. and the ASEAN nations respectively. It accounts for approximately 10% of China's total annual gross trade volume according to Xinhua.

On the other hand, China is Japan's largest trading partner and has been since 2007 when Japanese corporations dropped the U.S. market like a hot potato. China is also Japan's single largest export destination, accounting for nearly 25% of total export volume as well as the single-biggest source of its imported goods.

The damage won't be limited.