Yanagihara Tomomi teaches biology at protagonist Kotaro Makimura's high school. Students call her "Tomo-chan," a nickname she dislikes. Her professional demeanor frequently gives way to self-proclaimed "mad scientist" tendencies, fueled by an intense fascination with supernatural phenomena and mystery animals that derails classroom lessons. This paranormal expertise positions her as Kotaro’s trusted advisor when he experiences unexplained time jumps. She dubs his involuntary time-skipping "Daydrop" and guides him through these disruptions.

She maintains a perpetually unkempt appearance with short brown hair often styled in a messy, just-awake look featuring one distinctive antenna-like strand. Thick glasses and a white lab coat over standard attire like skirts and pantyhose complete her look. Beneath her initially plain and disheveled presentation lies an underlying attractiveness that emerges with minimal makeup, while her shorter stature remains constant.

Her personality merges intellectual curiosity with playful confidence. She acts as a supernatural "walking dictionary" with a sharp mind and mischievous streak, deliberately complicating situations for Kotaro and his friend Takeshi. A flirtatious dynamic with Kotaro leads her to embrace lighthearted banter, showcasing notable self-assurance. Crucially, she approaches Kotaro’s time-travel experiences without skepticism, accepting his explanations while offering pragmatic solutions.

Narrative involvement varies across adaptations: the OVA confines her to a supporting advisory role, while the original visual novel expands her importance. Her unique route diverges early from the main storyline, featuring substantial original content distinct from overlapping paths like Kaho’s or Ai’s. Consistently, she provides scientific or pseudoscientific context for time-travel mechanics, serving as both mentor and complicating factor in Kotaro’s attempts to alter tragic events.