Saki Aikawa works as a Tokyo police coroner and forensic specialist, handling multi-jurisdictional troublemaker cases. She analyzes crime scenes, examines evidence including footprints and video footage, and reports findings to investigative units like Materials Compiling Group No.3. Her expertise in footprint identification and video forensics proved instrumental during the Lemmings Incident and Human Knots case. While her assessments guide investigations, she maintains professional skepticism—acknowledging limitations like potential illusions even with seemingly unaltered video evidence. Physically slender with dark hair, she typically wears a braided ponytail over her right shoulder. Several bangs frame her face, secured by left-side hair clips. Her left ear bears four earpieces. She dons a manufacturer coverall and pants, often with multiple buttons undone to avoid tightness-induced cleavage exposure—a point of contention with colleagues. Accessories include a black fanny pack on her belt and a "coroner" armband on her left arm. Her personality exhibits consistent calm professionalism and emotional detachment. She maintains a straight face in diverse scenarios: encountering shirtless colleagues, enduring flirtatious behavior from peers like Tsubaki Iwanome, or confronting absurd incidents. This composure extends to high-stakes situations, including witnessing embarrassment over operational failures like Phantom Solitaire's escape. She once displayed subtle intuition by sensing Lemmings' proximity but dismissed it after finding no visible anomaly. Her chronology includes key casework: During the Lemmings Incident, she matched footprints at the Human Knots scene to Lemmings and reported inconclusive video analysis from Shakuzawa Building skeleton sightings. Later, she identified a female shoe imprint on Detective Kōzaburō Arase's chest as matching the Human Knots case. She arranged private treatment for his injury to conceal his visible yakuza tattoo from colleagues. After Lemmings encounters, she corroborated colleagues' accounts through evidence review and relayed Mikoto Saimyouji's occultist claims for further investigation. In Solitaire's Escape, she deadpanly highlighted police vulnerabilities when gag orders failed against internet leaks during briefings. Interpersonally, she shares a childhood acquaintance with Tsubaki Iwanome but responds matter-of-factly to his remarks, refuting suggestions of his "better big brother-type" role. She interacts professionally with Arase, assisting his injuries while acknowledging his background. With Ranmaru Yatsu, she recognizes his protective concern for his sister as "good big brother" behavior despite his self-conscious explanations. Her surname combines "mutual, reciprocal" (相) and "river, stream" (川). Her given name incorporates "bloom, blossom" (咲) and "princess, noblewoman" (姫).