Astraea is a very large-chested "Close-Combat Angeloid, Type Delta" (地戦闘用エンジェロイドタイプΔ（デルタ）?) sent by Synapse to kill Tomoki. She is strong in combat and emotion compared to Ikaros, but because of that allocation, her weakness is her low processing power, and the other Angeloids consider her an idiot; this is affirmed when she bungles her multilple chances to kill Tomoki at the Buddhist temple, and later at the quiz show where she fails basic questions such as "what is 1+1".. She is often famished because she does not know how to hunt or to obtain food by her own means; in one episode, she eats Sugata's fish bait.. After spending time with Tomoki, she refuses Master's order to kill Nymph, and severs her own chain.
Astraea has a good relationship with her senpai sisters. Astraea eventually realizes that she too has fallen in love with Tomoki, Chaos questions her on the definition of love. In recent chapters, she becomes depressed from losing her weapon and shield, but is encouraged by Tomoki who tells her only she can decide whether or not she is useless. She then decides to rescue her younger sister, Chaos.
According to Daedalus, Astraea is extremely quick and has great close-combat capabilities but is vulnerable to long-range attacks. She wields a super-osciliating photon blade called Chrysaor(クリサオルKurisaoru?), which can even penetrate Ikaros's Aegis defense system. For defense, she uses Aegis L (イージス LĪjisu Eru?, "L" stands for "left", as it appears on her left arm), a shield that is more powerful than Ikaros's version, but guards a limited angle and can only be deployed for a short period. However, in her fight with Ikaros Melan, Astraea's sword and shield are destroyed.
Astraea is named after the Greek mythological figure Astraea, who was a goddess of justice that later became the constellations Virgo and Libra.
