Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you'd like to add some Japanese stocks to your portfolio, the iShares MSCI Japan Index ETF (NYSEMKT:EWJ) could save you a lot of trouble. Instead of trying to figure out which companies will perform best, you can use this ETF to invest in lots of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The iShares ETF's expense ratio -- its annual fee -- is a relatively low 0.53 %, and it yields nearly 2%.

This ETF has not performed well, as Japan's economy has long been struggling. It didn't beat the MSCI EAFE index over the past three, five, and 10 years. Still, it's the future that matters more than the past, and investors with conviction need to wait for their holdings to deliver.

With a low turnover rate of 3%, this fund isn't frantically and frequently rejiggering its holdings, as many funds do.

Why Japan?
It's good to diversify your portfolio geographically, and Japan's fortunes may be turning around, in part due to its new, aggressive prime minister. The Nikkei has been rising, and the yen has dropped recently.

More than a handful of Japan-based companies had strong performances over the past year. Mizuho Financial Group (NYSE:MFG), for example, surged 31%, and recently yielded a solid 3.2%. Japan's second-largest lender's latest earnings report featured earnings up more than tenfold, due to a surging stock market boosting the value of its equity holdings. Lending profits were up 6% over year-earlier levels.

Nomura Holdings (NYSE:NMR), one of the largest banks in the world, gained 25%, despite losing its CEO and COO last year due to an insider-trading scandal. The company recently posted earnings that were a bit disappointing but still up 13%, and it has high expectations for its investment-banking business in 2013.

Other companies didn't do as well last year, but could see their fortunes change in the coming years. Nippon Telegraph and Telephone (NYSE:NTT) gained just 1%, but it's looking attractive to some, with a recent 4.3% dividend yield and its subsidiary NTT Docomo reducing its debt. But it faces strong competition, such as from Softbank, which recently invested in Sprint Nextel.

Canon (NYSE:CAJ), meanwhile, sank 21%, but offers a hefty dividend of 4.2%. The company has posted some disappointing numbers in recent quarters, but it compares favorably on a number of measures with many competitors. Boding well, though, is its patent strength. Canon has been one of America's top five patent holders for 27 consecutive years. It recently released a new Mixed Reality 3-D headset, and has been taking market share from printer rivals such as Lexmark.

The big picture
A well-chosen ETFcan grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.