Despair Dolls (絶望の獣 Zetsubou no Kemono?, lit,. "Beasts of Despair"), also known as D2, are grotesque creatures that were born from a "black meteorite" that descended onto Earth. They can assume a variety of forms, but they share a common trait of having a "mask" covering the black stone inside their body. They respond to music with aggression, and will attack any human playing music without fail.
The D2 are almost indestructible, unable to be killed by conventional weapons. This changed when the Symphonica created Musicarts, which turned the tables in the fight against the D2. According to Lenny, the D2's weakness is Harmonia Ore, which counters the Black Night Siderite from which they were made from.