Alongside well-versed safe havens gold and gilts, Japanese Smaller Companies was one of the best performing IMA sectors over the summer months, up 4.36%.
In addition, the top three performing funds in the IMA unit trusts and OEICs universe were all invested in Japanese equity.
FE Analytics, said: "Not only did these funds provide some sunshine during an otherwise dismal summer, but they have also rewarded investors over the longer term."
The top performing fund in the three months to 31 August was Legg Mason Japan Equity, which returned 21.7% in the period.
Over three years to 31 August 2011 the total returns of the fund were 62.73%.
Meanwhile, JP Morgan Japan saw returns of 12.1% in the summer months and 24.71% over the last three years.
Finally, Fleming Family & Partners Japan Equity returned 10.77% in the last three months and 23.36% over a three-year period.
European equity was the worst performing asset class over the summer, with the IMA Europe including UK sector down 15% and the IMA European Smaller Companies down 15.13%.
Pascal Dowling, investment specialist at FE, said: "This research highlights in bold print the value of diversification. Japanese equities, so long in the doldrums experienced a tremendous rebound this summer, but it’s worth bearing in mind the context of that bull run.
"Investors abandoned Japan in droves as the full extent of the catastrophic tsunami and subsequent nuclear accident became clear, wiping nearly 20% off the Nikkei 225 virtually overnight.
"When the water had receded and the nuclear crisis was under control, many investors took advantage of low valuations in Japan and bought in."
Dowling added that the combination of disaster in Japan and the unfolding debt crisis in Europe saw risk appetite and equity markets plummet.
As a result gilts, which were tipped by many at the start of 2011 as the big losers for the year, have performed steadily, with the IMA UK Index-Linked Gilts posting returns of 4.69%.
Standard & Poor’s Fund Services said global fund managers still disagree on Japan, however, with stockpickers far more bullish than top-down managers.
"Around one third of the funds considered in our review had overweight positions to Japan, mostly the result of bottom-up stockpicking," said Susan Sworn, lead analyst at S&P fund services.
She said the most highly exposed fund to Japan is the Warburg Value fund, managed by Credit Suisse’s Gregor Trachsel and Sven Sommer, with an absolute exposure of 34% of assets.
"The managers’ highly specific investment philosophy combines a contrarian, deep value approach, with statistical and fundamental industry and business model analysis and portfolio exposures are the result of bottom-up analysis alone, unconstrained by sector or regional limits."
