At first glance Fast Retailing Co, operator of the Uniqlo casual clothing chain and Japan's largest clothing retailer, appears to be on the crest of a wave.

Not only has it just booked record first-half sales and profits - net income surged 55.7% to JPY55.3bn (US$594m) while sales rose 31.8% to JPY470.9bn - but it also raised its full-year outlook.

Look behind today's numbers, though, and there are fears that these impressive figures fall a long way short of the retailer's own and very ambitious growth plans.

To try to stay ahead of the competition it has its eye on sales of JPY5 trillion by 2020 - against an expected JPY834bn in the year to August. 

And a persistent worry when it comes to achieving this target is that the retailer's business model currently has a sales skew towards its domestic market, with Uniqlo Japan accounting for a massive 76% of consolidated net sales.

While this has less impact when cash-strapped shoppers favour Uniqlo's low prices over more expensive department stores, it does of course have huge implications when domestic growth starts to slow.

And a focus on innovative ranges such as the company's HeatTech heat-retaining thermal underwear - of which 47m pieces were sold this year - puts extra pressure on the firm to come up with a steady stream of hit ideas.

The company has already admitted it is pinning its hopes for second-half same-store sales growth on new lines like Silky Dry and Sarafine innerwear which are in the pipeline for summer, as well as its UT printed T-shirts and the +J collection with fashion designer Jil Sander.

But it's a fine balance, as illustrated all too well in March when a spell of unseasonably cold weather in Japan led to a 16.4% drop in Uniqlo same-store sales.

The retailer is also struggling to replicate the success of Uniqlo in its other chains, such as the low-priced G.U. chain where T-shirts sell for JPY490 (US$5) and its Cabin women's fashion business.

And it's the same overseas, where work has been ongoing to try to turn around the Theory, Comptoir des Cotonnier and Princesse Tam.Tam operations.

Of course Fast Retailing already has plans to accelerate its overseas expansion, with its first store opened in Russia last week and its largest store in Shanghai, China due to open next month.

But while it has struggled to make its mark in the US and Europe, the powerhouse of its future growth are Asian markets such as China, Hong Kong, Korea and Singapore, where it has just added another 32 stores.

Ironically these are also the markets where competitors such as H&M and Inditex, owner of the Zara fashion chain, are hoping to bolster their sales as western markets continue to be buffeted by the aftermath of the recession.

Fast Retailing's regional knowledge could well give it an edge in these markets; but it may well have another trick to see off the competition after admitting earlier this year that it has US$11bn (JPY1 trillion) to invest in global mergers and acquisitions.

Click here for Fast Retailing’s first-half results.