>>2116716
When the Honshu clans declare on you just turtle up and rape their sieging armies with small gun garrisons. While you hold them at bay with a skeleton crew, consolidate Kyushu and take the southern trade nodes. You want to build up to max stack trade fleets on every southern node while your nanbans form a wooden wall (literally, you want a bunch of stacks of 1 of them just close enough together so no one can go around them)

Also pro-tip, ship cannons were massively nerfed in the last S2 update, but if you still want the massively expensive upkeep Black Ship for style points, you can capture it as soon as it spawns via autoresolve with 19 trade ships.