Sirene is one of the first demons to appear in Devilman, as well as one of the most commonly appearing. In the time before man she was a close confident, and sometimes lover, of Amon. In the present, however, she has nothing but hatred for him after he decided to side with humanity. While powerful, she is unable to kill the Devilman, and even after fusing with the demon Kaim she still dies before managing to finish him off. She also has a nasty habit of being hit with her own flying limbs.
In the Devilman Lady manga Jun and Akira run into Sirene on their journey through Hell. Still merged with Kaim and incredibly powerful, Sirene has risen to a position of great power in Hell, but still resented Devilman for killing her. She fights with him again, but only barely loses, possibly out of her love for Amon. Unable to live with her conflicted feelings, she requests the demon Medusa to turn her to stone.
Later, after Mao Dante rallies all of Hell to follow him back to Earth, Kaim begs the healed Medusa to restore Sirene to life. Her spirit returns to Earth where it merges with the recently dead body of Devilman Noir.
Lan Asuka is the overseer, mentor, antagonist, and (in her own mind) lover of Jun Fudou in the Devilman Lady anime. She orchestrates the world-wide fight against Devil Beasts while at the same time attempting to exploit her unique immunity to the Beast gene to become more than human. Her plans are halted only a day after claiming dominion over all of Earth when she is cut in half by Jun. While her hermaphrodite nature and assension to godhood would peg her as being Satan, she shows her true colors as her universe's version of Sirene in her final battle with the Devilman Lady.
Sirene has metalic claws for forearms and legs. As well as being exceptionally strong they can be fired from her body and remotely controlled. She can fly thanks to her wings, and can also use them to blow immense gusts of wind and create tornadoes. In her OVA appearance she gains the power of psychokinesis on a wide scale, as well as what is possibly the ability to create nuclear fission on a smaller scale. Her Lan Asuka incarnation adds the ability to control lighting to the list.
In the Devilman anime Sirene stands a dozen meters tall normally, but can also change her body, disguising herself as Miki or dispersing her body into a group of butterflies.