Tosa (土佐, namesake: Tosa Province) was a battleship of the Imperial Japanese Navy. She was laid down as the second Kaga-class battleship under the ambitious 8–8 Fleet Program. However, following the Washington Naval Treaty, all capital ships built after the Nagato class had to either be scrapped or converted into aircraft carriers. Unlike her sister ship Kaga, which was eventually converted into a carrier, Tosa did not survive the treaty restrictions. The Kaga-class design incorporated lessons learned from WWI, particularly the Battle of Jutland, which had not influenced the earlier Nagato class. Major changes included a revised armour scheme and the addition of an extra main battery turret.

Named after the former province on Shikoku, Tosa was laid down on 16 February 1920 and launched on 18 December 1921. Construction was halted on 5 February 1922 following the signing of the Washington Naval Treaty, and she was officially cancelled in April 1924. Her incomplete hull was later used for live-fire testing of armour protection and new shell types, trials that proved highly valuable for future Japanese warship designs. Many components were reused in other vessels, and her turrets were used for land fortresses. On 9 February 1925, the remainder of the hull was scuttled in the Bungo Strait, making Tosa the last Japanese capital ship disposed of under the treaty’s terms.

The IJN Tosa was introduced as a prize for the 2025 Winter Concert event. As a successor design to the Nagato-class, she carries an additional 41 cm twin turret, giving her a total of ten main guns. Her armour layout differs: instead of the layered belt of 4.5 inches, 12 inches, and 9 inches, Tosa features a uniform 11-inch side belt. Deck protection was also significantly improved, reaching up to 4 inches against plunging shells. She can reach a respectable 26 knots. Her greatest drawback, typical of many interwar designs represented in their as-designed configuration, is the near-total absence of AA defences.