Sumi Sakurasawa, a college student employed as a Diamond agency rental girlfriend, presents as quietly reserved with reddish-pink hair and eyes. Her early interactions rely on expressive gestures, sign language, and written notes, concealing social anxiety she aims to conquer through her profession. This choice stems from a deliberate pursuit of self-growth, pushing her to confront communication barriers by meticulously scripting dates and social scenarios. A spin-off manga further unravels her private struggles, unveiling a hidden ambition to become an idol—a catalyst for joining the rental service.

Guided by Chizuru Mizuhara, Sumi’s mentorship introduces her to Kazuya Kinoshita, with whom she practices vocalizing emotions during rehearsed sessions. Their dynamic shifts from professional collaboration to mutual emotional support, particularly as Kazuya navigates Chizuru’s personal challenges. Sumi’s emerging assertiveness surfaces in urging him to prioritize Chizuru’s needs, reflecting deepened empathy.

Standing 156 cm, her style favors pink hues across outfits and accessories, often paired with a signature right-side braid. A habitual overthinker, she mentally rehearses interactions, balancing caution with deliberate intent. Her surname, meaning "cherry blossom marsh," and her dog Suzuri ("inkstone") subtly mirror themes of transient beauty and adaptability.

Later narratives place her at the periphery of Kazuya’s film project, where quiet encouragement becomes her contribution. While gradual confidence emerges in social spheres, her gentle introspection remains central, positioning her as a stabilizing counterpoint to bolder personalities. Familial ties stay unexplored, her focus anchored in self-reinvention through persistent, understated resolve.