Online brokerage Monex Inc. said Wednesday it plans to absorb Saison Securities Co. of the Seibu Saison retail group next year to become Japan's No. 3 online brokerage service provider in terms of number of accounts managed.

Monex, established in 1999 by Sony Corp. and other investors, will also tie up with another member of the Saison group, Credit Saison Co., the largest consumer credit-card issuer in the nation, the company said.

Details of the tieup have not been decided, but they will likely include an arrangement allowing Credit Saison card holders to deal online with Monex, it said. The plans were approved at the companies' respective board meetings the same day.

Monex said it will first make Saison Securities a wholly owned subsidiary on April 1 through a share swap.

Monex will float new shares to be exchanged for all of Saison Securities' outstanding shares. Each Monex share will be exchanged for 171 Saison Securities shares. The number of new Monex shares will be about 5 percent of its outstanding shares.

Monex will then absorb Saison Securities as soon as possible after the deal is completed, it said.

With Monex's existing 100,146 accounts and Saison Securities' 50,360 accounts, the merger will make Monex the third-largest online brokerage in Japan, following Nomura Securities Co. and Daiwa Securities Group Inc.