Mei Tachibana is a police officer working at the Banzai Bridge Police Station in Akihabara, who refers to herself as a super cop. She is a young woman with a striking appearance, sporting short black hair and yellow or gold eyes, and is most often seen in her police uniform. Standing 165 centimeters tall, her physical presentation initially suggests a competent and attractive public servant, though this facade quickly gives way to her true nature.

The core of Mei's personality is a profound and erratic obsession with anything she deems cute, a category that adheres to her own peculiar and often disturbing criteria. She is an unstable individual prone to sudden mood swings and displays a notable lack of empathy when pursuing the objects or beings that capture her interest. Her duties as a police officer are entirely secondary to her self-appointed mission of collecting, a euphemism for theft that she sees no reason to hide. She will brazenly confess to her crimes, believing her actions are justified by her personal aesthetic whims. While on duty she is volatile, she appears to be calmer when off the clock, and she openly admits that her career choice was motivated by the stability of a public servant position rather than any sense of justice.

Mei's primary role in the narrative is as a recurring antagonist and source of chaos, driven by her uncontrollable acquisitive desires. The most significant target of her obsession is Jashin-chan, a demonic lamia. Upon their first encounter, Mei immediately falls in love and, abusing her authority as a police officer, attempts to claim Jashin-chan for herself, affectionately but unwelcomely rechristening her Orochimaru. This unrequited crush becomes a running gag, with Mei persistently attempting to capture Jashin-chan, sometimes resorting to violence when her affections are not returned. Her other key relationships are similarly defined by her fixation. She has repeatedly kidnapped the mole-like creature Koji, planning to either stuff her or preserve her in formaldehyde due to her perceived cuteness. She has also detained and tried to collect Pekola, mistaking her for a human child, and has attempted to steal Ran-ran, a talking panda doll. At the police station, her colleagues find her bizarre behavior off-putting, simply labeling her as the quirky one. Feeling sidelined by newer characters, she has formed a rebellious alliance with the demon Yusa to reclaim the spotlight.

In terms of abilities, Mei wields the equipment of a police officer, including a handgun, handcuffs, and has been known to use grenades and a switchblade. She also possesses a surprising amount of physical strength, capable of carrying large statues or ripping out grave markers to add to her collection. Her combat ability is noted to be among the highest in the series when she is in collecting mode, though her actual effectiveness can be hampered by her erratic nature, such as firing her weapon in a random rapid-fire fashion. There is no significant character development for Mei within the series; she remains a consistently selfish, powerful, and obsessive force whose primary motivation is satisfying her own skewed definition of cute, whether that be a statue, a traffic sign, or another living creature. A noteworthy example of her behavior is when she first met Jashin-chan; after being refused permission to keep her, Mei decided that if she could not have Jashin-chan, no one would, and she attempted to kill her with a telescopic sword.