This stage starts with a Two Can. When the castle is damaged, Bun Bun Black appears as the boss and Two Can, Le'noir and Tackey as support.
Stall the first two-can until you get enough money. When the boss appears, keep spamming Island Cat, Manic Island Cat and Dark Laser against the enemies. Time your Bahamut to inflict heavy damage against the Bun Bun Black and defeat the Two-Cans.
If you have Immortal Keiji, then this stage becomes much easier.
Start off by spawning Keiji and spamming your meatshields. The Two Cans' shockwaves won't even hurt him.
By the time the base gets attacked, you may not even need meatshields. By the time Keiji dies, you should at least almost have another one recharged. Once you finish the enemies, you've won.
After a "legitimate" completion, KevN23 used a much dirtier strategy to beat the stage quite easily. He used Skelecat + Mr. + Necromancer for a 2 second decrease in production time and proceeded to win by simply spamming Kasa Jizo. The CatCombo "Aerial Recon" could be used to even better effect.
With the help of Rice Ball cat, A bahamut, and Zamboni Cat to perfectly kill the initial Two-cans and then stack Ms. Signs until the enemy limit is reached, then knock those back behind the base and win.