Siren appears to be a simple construction that is reminiscent of a singular loudspeaker. A distinguishing this creature from the standard electrical appliance is a distinctive linear patterning that is present on the surround, but by far its most characteristic feature is that of a cloaked female and angelic form, that is integrated into the electronic component of the structure by both its hands and torso.
Sound (音, Oto): With a deafening scream, the Siren can use a powerful blast of dense sound waves to repel an attacker or attack. This was capable of pushing back Black☆Star while under the effects of Madness Takehold.
At some point, Siren was founded by Noah and consequentially captured and imprisoned within the Book of Eibon.
Siren was later summoned to defend Noah from both Death the Kid and Black☆Star, with the Siren blowing away the assassin. She is later summoned back into the Book of Eibon after.