It was founded in 1965 as Toyo Agency (東洋エージェンシー, Tōyō Ējenshī),[1] with it being designated by baseball team Yomiuri Giants as its primary agency for the planning and distribution of the team's merchandising interests.

[1] It has been involved in the production and licensing of numerous television programs, beginning in 1972 with Thunder Mask.

[1] In October 2019, Bandai Namco Holdings announced plans to acquire Sotsu, a move which would grant the company rights to the entire Gundam franchise.

[2] The next month, however, Chicago, Illinois-based investment firm RMB Capital forced Bandai Namco to raise the tender offer price for Sotsu in a follow-on tender offer targeted at the general shareholders of Sotsu.

[3] On March 1, 2020, Sotsu finally became a fully owned subsidiary of Bandai Namco.