Heaven's Ruins

Head for the research lab in Second Miltia, and use the Sequencer A on the forbidden device downstairs. Once you reach your destination, just go forward, while destroying the crystal statues on both sides to get a Bio Sphere and a Med Kit M. In the next room, there's a save point directly ahead. Use it if you want. Now go forward until you reach a path with a block on either side. Blast the one to the right, proceed along this path,destroy the block at the end for a treasure chest containing Secret Key 31.

Go back a bit, then head left at the fork you previously ignored. At the next fork, go north then east. Destroy the block on the other side when you reach the end. Head back, then south at the fork onto the large platform to fight the first of 3 mini bosses.

Boss Battle - Svarozic

This enemy is fire-elemental, so equipping Flame Coat on your characters is a very good idea. Casting Flame Veil also helps. Now cast Ice Sword and Attacker on your party, then start unleashing combos. One more thing, it occasionally uses Flame Blast to heal.

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A red sphere will appear at the upper section. Go there and destroy it to activate the red sphere at the giant door in this room. Afterwards, make your way back to the very first fork in this area (the one with blocks on both sides) and destroy the left block. Head right at the fork. Defeat the enemy here, and go north. Blow up the block for a treasure chest containing Skill Upgrade E (x6). Now exit through the eastern passage. Here head north at the fork, then west near the end of the path through another passage.

In this room, blow up the block at the end of the path, and go back to the previous area. Proceed onto the large platform to fight another mini-boss.

Boss Battle - Peran

Equip Thunder Coat and cast Thunder Veil on your party. Next cast Aura Sword then Attacker. Unleash combos. It casts Thunder Blast to restore about 1600 HP. Also, remember to move one of characters behind this boss, for additional damage from "Back Hit".

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After that, make your way back south, then east. Follow the path and smash the yellow sphere at the top -- to activate the yellow sphere on the door at the main room. Return to the main room and save your game. Now, proceed to where you fought the first mini-boss, and head northwest into the next room.

Boss Battle - Stribog

This one is ice elemental, and at the same time, all of its attacks causes L Slow. Equip Ice Coat and cast Ice Veil on your party. Its a good idea to use Ziggy here, since he has fire as his element by default. As for your other characters, cast Flame Sword then Attacker. Start using combos afterwards.

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Head back to the main room, and proceed to the part with exits in both left and right sides. Take the left one. Smash the blue sphere. Return to the main room, save and exit through the newly unlocked door. Here keep heading up the spiral path. Then go out and head east at the fork. You'll a gnosis standing there, waiting. These things are really tough, but you'll have to defeat them in order to proceed. You can choose to beat them the EASY way, or the HARD way. I'll go with the easy way, since the hard way, is well REALLY hard, so I don't think it's worth explaining here.

Make sure that Shion is positioned behind the boss at the beginning of the battle. Keep escaping until you get the formation right. Then cast both Aura Sword and Ether Spear on Shion (actually the just Aura Sword will do) and summon Erde Kaiser Fury, to get this over with.

Head back and continue along the spiral path. When you reach the second layer, destroy a part of the wall to find Segment Address #12. Continue up, then proceed down at the fork for another set of those things. After that, climb up again and save. Continue through the passage and approach the little thing for another mini-boss fight.

Boss Battle - Zwerg Cape

There are 5 of these things, which must all be defeated at the same time. Equip Aura Coat and Hammer Coat on your party. Bring Ziggy in (for his default fire element) then cast Flame Sword on your other 2 characters. Now attack each of these enemies, until they have about 1600 - 1700 HP left. Then finish them off with the Fiery Ritornelle double attack. Alternatively, you can just summon Erde Kaiser and be done with this fight.

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The platform will take you up to the next area. I suggest that you head back down and save before fighting the real boss for this dungeon.

Boss Battle - Nepos Rigas

First, equip Spear Coat and Hammer Coat on your battle party. When the battle begins, cast Aura Sword and attack to build up your boost gauge. Stock everyone to full, then start doing combos. Both Dual Spell Ray and Phoenix Blade double attacks deal pretty serious damage here. Each do no less than 7200 and 14,000 HP worth of damage respectively (non-critical), while the boss is suspended in mid-air. So I recommend using them if at all possible.

Once you've done enough damage, it'll put up a shield which gives it "Break Block". Just rely on Aura Sword and Attacker to boost your attack power at this point. It also has a deadly fire-based move called, Ragnarok which is something you should worry about. (Fire Coat & Veil is a good way to reduce damage from that one.) When you see the messages "the door to ruin opens" and "fate is inevitable", be prepared since Ragnarok will definitely follow.

When it's down to about 10,000 HP, the boss will stand still and allow you to attack. If you fail to kill it in one blow however, it automatically counters with Embrace, killing the target instantly. This is the right time to bring in Shion, cast Aura Sword on her, and summon Erde Kaiser to finish it off.

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Open the treasure chest containing Decoder 12. Head back down and unlock the corresponding segment door, to get Sequencer D. Dive out of here using the green forbidden device. Now proceed to the Desert, and activate the multicolored forbidden device there, with the Sequencer D.