Investors who put their money in Stratton Street Capital LLP's warrant fund have been on a roller-coaster ride of late.

The fund, Japan's best-performing in 2015, plunged 25 percent on June 24 when the U.K. voted to leave the European Union, bringing its drop this year to 50 percent.

The fund, whose moves amplify the Topix index's performance, tends to fall about three times more than the benchmark when it declines and gain five to seven times when the index rises, Matthew Lonergan, who runs Japan Synthetic Warrant Fund with Trevor Sliwerski and Rowan Chaplin, said in an interview.