The IJN Tosa was a battleship in the Imperial Japanese Navy and the lead ship of her class. The Tosa class was developed as an enlarged version of the Nagato class, with an additional main battery turret and slightly weaker side armor. The Diet initially rejected the construction of these ships and a second Nagato-class ship. However, in late 1916, U.S. President Woodrow Wilson announced the construction of ten new battleships and six battlecruisers. Ultimately, his plan was only half completed. But following his announcement, the Diet approved the construction of the Mutsu battleship and the Tosa class.

Named after a province in the Shikoku region, Tosa was laid down on February 2, 1920, and launched on December 12, 1921. Construction was behind schedule, and funding was modest. Work on the battleship was suspended on February 5, 1922, before the Washington Naval Treaty was officially signed, and it was officially stopped in April. Tosa's hull was used to test her armor scheme, which later proved instrumental in future Japanese ship design. On February 9, 1925, the hull was scuttled in the Bungo Strait. Tosa became the last capital ship of the Imperial Japanese Navy to be destroyed in accordance with the Washington Naval Treaty.

The IJN Tosa was introduced as a prize for the 2025 Winter Concert event. The battleship has excellent main battery guns with powerful shells and a fast reload time. She also boasts decent maneuverability and numerous, powerful secondary guns. However, her armor is mediocre at best, and her anti-aircraft batteries are practically nonexistent.