ELMA-DS
One of the strongest viruses created by Mir, this creature is a dark version of Shurelia's own ELMA guardian, capable of brainwashing them and causing severe havoc throughout the Tower. Its appearance triggers the start of the story of Ar tonelico: Melody of Elemia, and its fought in four separate ocassions.
First Battle
This is the battle fought during the game's prologue, and while the ELMA-DS has exactly the same stats as during the actual first battle with it, it's an scripted battle that can't be won. During this battle, the only thing you can do is make Lyner and Ayatane attack it a couple of times until Shurelia releases her Primal Word Song Magic, which forces the ELMA-DS to activate its Flip-Flop Conversion abilities and makes it completely immune to any attacks. After this, it uses its Harm Wave attack, which can't be blocked this time, and the battle instantly ends.
Second Battle
This is the battle fought at the Symphonic Reactor, which will have one of the two versions of EXEC_PURGER/. as the battle theme depending on who you chose as the receptor for Downloading the Hymn Crystal Purger. During this battle, the ELMA-DS can use four attacks: Bugs Fang, which causes average physical damage to a single target; System Break, which severely lowers all the stats of the party; Cross-Cut, which deals large physical damage to a single target, and finally, its most dangerous attack: Harm Wave. This is the first Lv. 3 Stored Attack featured during the game, and as such, causes large amount of damage, and will most likely kill off your Reyvateil if you fail to cover even one of the target rings.
As its System Break can greatly weaken your party, try to counteract it with items like the Megamilk or Opal Rice, and try to use the best skills and Song Magic you have available at that point. Likewise, always pay attention to whenever it tries to use Harm Wave, and be ready to protect your Reyvateil, which will allow you to unleash one of the Super Counters of your party members, dealing large damage and allowing you to defeat it faster. Since the battle is interrupted once its HP reaches zero, you won't receive any experience, Leaf or items from defeating it.
Third Battle
This is the battle fought inside Aurica's/Misha's Cosmosphere, depending on who you chose for the Download of the crystal, and it also serves as the final boss battle for Phase 1. This battle is pretty much identical to the previous one, except for the fact that the ELMA-DS is accompanied by a trio of ELMAs, so take care with them. Try to dispose first of the ELMAs, and then apply the same strategies as the previous fight with it.
Fourth Battle
This is the battle fought in the S.P.U., and it's also the final time you will face ELMA-DS. The background music for this will be the EXEC_PURGER/. version of the Reyvateil whose path you chose at the start of Phase 2. At the very start of this, the ELMA-DS will summon three ELMAs to help him, and will also use the Duplicate ability to resummon them whenever they fall, so you should ignore them and concentrate on the main boss. Luckily, it lost its System Break ability in order to be able to use Duplicate, so you won't have to worry about debuffs, but still it can cause large damage, so try to keep your party healthy and attacking to take it down.
Other Appearances
Shurelia can summon an ELMA-DS whenever she uses the highest Burst Lv. versions of her ELMA-DS Song Magic. This iteration of the ELMA-DS uses the Harm Wave attack to deal Ice-elemental damage to all enemies.