Boss - Quiet Ku
It is best to attack this droid with elemental magic: fire and water. Physical attacks do little against him. Please note that whenever he enters Gunman Mode, he gains the ability to effectively resist your attacks. If you want to avoid losing a lot of health, do not attack him at this time.
Go through the south door to get the Ancient Feather. Now go east and turn off the other engine. The next blue laser has been deactivated, so follow the newly opened passage.
Boss - Turbulent May
This droid has two special techniques: Turbulence (spoils your formation) and Foresight (works similar to Ku Fist Arrow Mode). The key to victory, again, is black magic.
Another engine can be turned off south. Return to the intersection and continue. Destroy the two groups of droids guarding the door and take the Thief's Path from the chest, as well as the Supermetal Earring. A little further you will see a room with three chests (Shadow Crystal, Mega Magical Medicine, Ultra Medicine), a storage point and a regeneration machine. Use the latter. Go through the next door. Behind him you will see a group of monsters (Double Ax - this guy has a lot of health!). Do not use items in this battle - then just go back to the healing machine. Turn off the other engine and turn back to meet the next boss.
Boss - Heat Sai
This battle is usually very similar to the previous ones. Whenever the enemy holds a bomb in his hand, try to aim (Jiro will offer it after a few rounds). Thus, you will do more damage to the enemy.
After the battle, use the healing machine again and return. Go through the recently opened passage (next to the room where you found the supermetallic earring). In the next corridor, turn right and take the Great Crystal of Light from the chest. Pass to the next level right through the corridor. Before going there, get to the end of the corridor to find an iridescent cyclone and a supermetal necklace. Go back to the door. You will find a deformation device there.
After using the warp device, go down and use the save point. Now you will encounter the last droid of four.
Boss - Mad Kesu
Similarly, again, basically. This witch casts negative status spells on your group and can deal damage to all characters at once. The magic of fire, water and wind will bring you success here. Titan Gel Gold