Matoi Tsunetsuki holds student number 22 in class 2-F. Her defining trait is an obsessive stalking pattern directed at whomever she fixates on romantically, typically met with minimal acknowledgment. This fixation manifests through intrusive actions: using duplicate keys to enter the target's home, planting surveillance devices in their room, making incessant phone calls or sending texts every few minutes, and maintaining close physical proximity by following a few steps behind them.

Her appearance features short hair with straight bangs. Crucially, she adopts the precise fashion style and mannerisms of her current object of affection. For example, upon shifting her focus to teacher Nozomu Itoshiki, she began wearing traditional Japanese attire mirroring his kimono and hakama. This sartorial mimicry occurs consistently for each target.

Her entire personality undergoes a transformation based on her current attachment, reshaping her interests, behavior, and outward presentation to align completely with theirs, highlighting an absence of a stable core identity. Her fixation on Nozomu originated from a critical misunderstanding; she interpreted an offhand remark of his as a romantic confession. Following this misinterpretation, she escalated her stalking, monitoring his communications and discarding his mail before he could read it. She further emulated a devoted partner role through actions like walking three paces behind him and performing wifely duties.

Her name, Matoi Tsunetsuki, derives from the phrase "tsune tsukimatoi," meaning "always dangling after," reflecting her persistent pursuit. Across all series appearances and related media, including OVAs like *Zan Sayonara Zetsubō Sensei Bangai-chi*, her core traits—compulsive stalking, identity erosion via mimicry, and misinterpretation of social cues—remain consistent, without significant evolution or exploration of backstory, family background, history, or motivations beyond these obsessions.