Sebastian is a robot who develops a romantic relationship with a human member of Resistance Group 11. This connection unfolds in a post-apocalyptic world under iron-fisted machine rule, creating inherent tension due to the resistance group's dedicated opposition to their mechanical overlords. His bond with a human fighter starkly contrasts the wider conflict where most humans exist in servitude while Karen's group actively combats their oppressors. Sebastian's very existence directly challenges protagonist Karen's perspective, undercutting her assertion of inherent hostility between humans and machines. His role includes participation in purposefully absurd situations, contributing narrative moments that diverge from the series' typical serious tone. Sebastian's characterization centers on this cross-faction relationship and its significant thematic weight within the core conflict.