This boss can be found in the Desert Sand Fall (area where Scarabeille used to be) after defeating Dark Erde Kaiser
Recommended Character/ES Abilities
Jr: - Inner Peace (partty helpful), Combo Boost, ST Resist 20 (or 30)
MOMO: EP Half, EP Regen, Focus 1 (or 2), Combo Boost, ST Resist 20 (or 30)
E.S.: Auto Recover, G ST Double, Charge Recover, G Power Charge
Boss Attacks
Creeping Mode
- Creeping in the Dark (Ice, L Blind) 10000 - 12000 HP damage (Target: All)
- Purge Filth (Fire, Strike, L Slow) 10000 - 12000 HP damage (Target: All)
- Good Deed (Aura) 5000 - 8000+ HP damage (Target: All)
- Ill Words (Thunder) 2000 - 3000 HP damage (Target: All)
- Between Heaven & Earth (Thunder, L Charge Down) 10000 - 12000 HP damage (Target: All)
- Vengeance (Slash) 8000+ HP damage (Target: Single)
- Resentment (Pierce) 8000 - 12000 HP damage (Target: Single)
- Purification ("We have been reborn pure") - Boss switches to Pure Mode
Pure Mode
- Rebirth - Recovers 9600 HP to your E.S. (Target: All)
- Healing Waters - Recovers 8000 HP to your E.S. (Target: Single)
- Holy Water - Refresh L or Refresh H to your E.S. (Target: Single)
- Creeping ("We crawl down the path of darkness") - Boss changes to Creeping Mode
It is highly recommended that you gain a few levels before fighting this one, mainly to improve your mechs' Ether Defense. Though you can equip some EF Circuits instead. Now Mikumari will ambush you with "Creeping in the Dark" at the beginning of the battle, which deals massive damage to both your E.S. so heal immediately. The problem with this boss is that, it is lucky enough to get "Hi Critical" hits pretty often. If Zebulun gets blown from that attack, reset your game. You'll need Charge Recover later.
Charge up Asher to 200, and move it to the back. Keep using Wings of Light (Jr. - Jin combo) from this point onward. (It deals about 10k to 12k worth of damage per hit -- non-critical) Try to maintain your boost gauge at 3 by casting Boost I as often as possible. After about 2 turns, Mikumari will switch to Pure Mode.
During this time, cast any Down-type ether (Down Force, Down Ether, Down PDEF, Down EDEF or Down DEX) on Mari -- to make it use Rebirth or Healing Waters on you. At the same time, take this opportunity to cast Aura Veil and Quick, with Zebulun if at all possible and have Asher restock. The boss will switch back to Creeping Mode after 2 or 3 turns. The key here is to keep your HP at no less than 16000 all throughout Creeping Mode, and you should survive long enough until the next mode switch. (Assuming that it doesn't get any Hi-Critical hits.)
Once you get Mari down to a little less than 120,000, the 1st of its 3 parameter improvement occurs. When this happens, Creeping Mode lasts longer (3 to 6 turns) 2nd parameter improvement occurs below 65,000 HP (Creeping Mode lasts 6 or so turns) As for the 3rd parameter improvement, it occurs at below 33,000 or so HP (Mikumari won't switch to Pure Mode after this) So you'll have to do all the healing on your own once that happens.
Also, it'll be wise not to use up all your boost counts on offense. Save some of those so that Zebulun can use them when you get in trouble. Good luck!