From Scratchpad

This Act is fairly short, but the boss battle at the end is very tough. I recommend that you level up and stay at zero percent experience, so you can constantly revive at the zone entrance. Remember to bring a full party, and be prepared to die.
At the beginning, you will be introduced to Setsu, Azura's older brother and a researcher for Central Command. He will hand you a special event plate for Cell Tower. Head out to Shibuya and head south to Cell Tower. It is the southern-most "D" on Shibuya's map.
This special dungeon is very simple. It only has one floor and one boss floor, with only two fights between the two floors. Your goal here is to talk to all six DB NPCs here. Everytime you talk to one, you should get an on-screen prompt. Once you have talked to six DB NPCs on this floor, move on to the boss floor.
On this floor, DB Mikanagi(DBミカナギ) and his devil will be waiting in front of the boss room entrance. Talking to Mikanagi is the only way into the room, but he will not let you in if you did not talk to all six DBs on the previous floor. Before you talk to him, be ready for the fight ahead. De-equip all blunt weaponary and summon devils that can resist fire, swords, or hama.
This is the big fight that I warned you about. You will be going up against one Power and several Archangels. As with many boss battles, these devils will home in on anyone who uses magic. Try to have all your party members ready to attack different Archangels before you use any magic.
The best way to finish this fight with minimal casualites is to take out the Archangels first. They are weak to Ice, Psyche, and Mudo attacks. Since the Archangels do gang-up on magic users, it may be best to have fighters buy the special elemental machettes and use them in this fight. Even with these tricks, you will still die a couple of times. Be patient and you will win.
The main boss is Power, and he will not stay still while you fight the Archangels. He will come at you with his spear thrusts, the Heatwave attack, Hama, or even Megido. Megido itself will take off well over a hundred and twenty HP, so try to keep your life in the green. Power is also weak against Psyche, but his high HP will keep him from dying too quickly. If you followed my instructions and took off any blunt weaponary, you will not have to worry about how Power reflects blunt force.
Once the battle is over, you will receive a two hundred thousand experience bonus, which will hopefully cover any experience loss you may have suffered earlier. If not, you will get another bonus when you report to Yamamoto. For a shortcut to Shinjuku, talk to Mikanagi, who appeared in the room after the fight ended. He will teleport you to the front of Central Command.
Once you reported to Yamamoto and received your experience bonus of five hundred thousand, you may think the Act is over, but there is still one thing left to do. You must leave Central Command. Doing so will allow you to see one final cutscene and will allow you to access Act Ten.