* Full Disclosure: I fought each of these Bosses afterI got the Maid Weapons in the Forgotten Village. Each Maid Weapon has an ATK of 900, making these and all other battles ridiculously easy. Because of this, I did not include a strategy for any of the bosses.
After the Normal End, and after you talk to Maidame Curie at Mount Ramah, there are four sign posts scattered around the four worlds, each with a special Boss, and a legendary weapon.
These bosses (and weapons) are completely optional - whether you complete this section or not will have no impact on the rest of the game.