Japan could not easily fund and crew enough battlecruisers for scouting and support duties while maintaining the battleships needed for the main battle line. Its large cruisers were meant to hold and damage enemy battleships long enough for surviving Japanese battleships to finish them if the battle went well. In defeat, the cruisers were expected to make an enemy victory far more costly. A fast battleship could perform part of that cruiser role and still fight in the battle line. The type answered a national resource problem as much as a design ideal.
Notable Point · 44:39-46:24
Why Japan moved toward the fast battleship
Japan's limited money, industry, and personnel encouraged a fast battleship that could contribute to both cruiser operations and the main battle line.