(Bloomberg) -- Rakuten Group Inc. shares surged on Monday after the Japanese e-commerce company announced that it would offer one-year free mobile plans for shareholders.

The 6.7% advance in the stock, its biggest in three months, takes Rakuten’s gains to about 39% since Japanese equities plunged in early August. The benchmark Topix gauge is up about 23% over the same period.

The mobile offer taps enthusiasm among Japanese retail shareholders for special deals, which was highlighted recently by Tokyo Metro Co. promising free train tickets and other perks to entice investors to its initial public offering.

Rakuten shareholders owning 100 or more shares on Dec. 26 will be eligible to the one-year mobile deal, the company said after the stock market closed on Friday.

The perk is a big incentive to buy the stock, particularly for families, said Travis Lundy, an analyst at Quiddity Advisors who publishes on the SmartKarma platform. Lundy estimates that the free plans are worth the equivalent of around 28% of the purchase price of 100 shares in Rakuten at Friday’s closing price.

He cautioned that the boost to the stock may be short lived, given that shareholders only need to hold the shares on Dec. 26 to be eligible.

While Rakuten reported a bigger-than-expected net loss last quarter, the negative impact from its mobile segment narrowed, as subscribers increased.

There are five buy ratings on Rakuten stock, nine holds and one sell, according to data compiled by Bloomberg.

(Updates prices for shares and Topix.)