Investing in Japanese financial companies has long been an extremely boring game. Since the Lost Decade crisis the Japanese economy has been driven by extremely low interest rates, and other than dividends, there was no real return to be had in Japan's major banks.

That could be changing, as Japanese economists express growing optimism about Prime Minister Shinzo Abe's reforms, particularly his plans to continue reducing Japan's corporate tax rate.

Japan's corporate rate stands at 38.01%, one of the highest in the world, and the Abe government plans to reduce that to a level below 30%, putting it more in line with other developed nations.

While picking winners and losers in this and other Abe reforms would be extremely difficult, the safe bet would be to look at those boring major banks again, which could resume growing if the Japanese economy does likewise.These include the enormous Mitsubishi UTJ (NYSE:MTU), Sumitomo Mitsui Financial (NYSE:SMFG), and the Mizuho Financial Group (NYSE:MFG).

Keiretsu: The Japanese giants
When we talk about any of these three, it's inevitable to consider their respective positions astride massive keiretsu, the Japanese form of interlocking companies that create conglomerates. These conglomerates dominate the Japanese economy, and if the reforms pay off big for them it is inevitably good for their banking firms.

The so-called "Big Six" such conglomerates are fully represented here, with Mitsubishi UTJ holding sway over the giant Mitsubishi industrial empire as well as electronics giant Sanwa. Sumitomo Mitsui Financial, as you might expect, represents financial and construction giant Sumitomo as well as chemical and shipping giant Mitsui. Mizuho Financial covers the powerful Fuyo as well as electronics powerhouse Dai-Ichi Kangyo.

Those names might not all be immediately recognizable, but the various components of the Big Six cover a huge portion of the big name Japanese firms whose products we regularly buy. I daresay if you name a random Japanese company most Americans have heard of, it's more likely than not to be within one of these six, and consequently is working hand in hand with one of these banks.

A quick look at the numbers
While investing in these companies is inevitably a bet on the Japanese economy finally returning to significant growth, it's also helpful to know where these three banks stand right now when we decide which, if any, to add to our portfolios.

Mitsubishi UTJ is widely considered the strongest financially as the second biggest financial company on the planet, and had the smallest hit when the Japanese asset bubble burst. It's trading at 9.25 times earnings, which is the highest P/E of the three, but at just 0.68 times book, it is obviously still a nice discount. They have the smallest dividend yield, at 2%, and the lowest return on equity at 8.47%.

Mizuho Financial, by contrast, took a worse beating in the asset bubble. That's inevitable because of their huge retail banking segment, and they've recovered nicely, with the highest profit margin at 26%, and the highest dividend yield at 2.6%. Their P/E is just 7.7, and they trade at just 0.78 times book value, with a respectable 9.61% return on equity.

Sumitomo Mitsui has the lowest P/E of the bunch, at 7.18, and the highest return on equity at just over 11%. They are similarly cheap, at just 0.82 times book, and sport a comparable 2.2% dividend.

The long and short of it
If you read through those numbers, you've likely noticed that all three of these stocks are trading pretty cheap, and are all pretty similarly valued. That's to be expected as all three are so inexorably linked to the Japanese economy itself.

In the end investing in one of the three over the others is a judgment call, and there's likely no wrong answer. It might even be worth considering diversifying across the three to get even broader coverage of the Japanese economy.

Ultimately, the Abe reforms are going to take time, so none of these stocks are likely to be overnight sensations. But with respectable dividend yields, any of them should be comfortable buy and hold target.