Gravity ( GRVY) surged 21% after controlling shareholder Jung Ryool Kim sold his 52% stake and set plans to quit as a director.

Gravity said the sale covered shares owned by Kim and his children, Jung Ryool Kim, Ji Young Kim, Young Joon Kim and Ji Yoon Kim. The buyers were Ezer and Techno Groove of Japan, a pair of technology ventures controlled by Nichiei Ryu and Taizo and Masayoshi Son.

The buyers said in a Securities and Exchange Commission filing that they might seek to increase their stake but said they wouldn't pay more than the $7.10 an American depositary share they forked over in the initial transaction. The buyers also said they might seek to delist the stock or sell Gravity's assets to a company they control, depending on market conditions and circumstances.

"We expect this sale to result in a change of control in us," the Seoul-based online gaming company said. Its shares rose $1.51 to $8.61.