She might be inspired of the legend of Arachne, a mortal weaver who challenged Athena, the goddess of War, resulting in her being transformed into a spider as a punition for her foolish behavior. Since the beta Arachne's model has been updated. But without a doubt Arachne is based off Rachnera Arachnera from Monster Musume No Iru Ichijou, hence the symbol on the back, human body, and the lavender hair.
Arachne was once a giant spider in the old beta, but has since been updated into a human form that resembles the top half of Arachne from in Greek Mythology.
Arachne's ability is to bind survivors in a web that immobilizes them.