Seiren

Seiren is an "Underwater Combat Angeloid, Type Eta" built by the man of Synapse that appeared in chapter 45 of the manga. Her appearance in the manga was brief, as she was impaled in the back by one of Chaos' wings before being devoured and absorbed by her just after she was ordered by the man of Synapse to kill Tomoki and Ikaros. Her appearance is based on the sirens of Greek mythlology.