Shizu Murasame, known as Oshizu, is the ghost of a girl who perished roughly 400 years ago amid a famine she recalls as a "living hell." While her specific cause of death remains unstated, implications suggest she might have been a ritual sacrifice intended to end a drought. For centuries, she lingered within the abandoned school building where she died, until encountering Rito Yuuki and his friends during their investigation. This meeting spurred her curiosity about the modern world beyond her haunting ground.

Her spectral form possesses long dark blue hair, blue eyes, a translucent body emitting light wisps, and a ghostly tail replacing legs. She dons a white kimono secured with a purple sash, tied right-over-left in the traditional funeral style befitting her deceased status. Scientist Ryoko Mikado later crafted a prosthetic biological body for Oshizu to inhabit, enabling physical interaction. This body replicates her ghostly appearance minus the translucency and possesses human-like measurements of 82-56-81 cm. When using this body, she typically wears a Sainan High School uniform or a pink nurse's uniform while assisting Mikado. Strong emotions like excitement or fear can cause her spirit to temporarily disconnect from this body, reverting her to ghost form.

Oshizu exhibits a sincere, kind, and intensely curious personality, particularly regarding contemporary life. Her Edo-period origins surface in old-fashioned mannerisms, such as using a Japanese brush for calligraphy. A defining trait is her severe cynophobia (fear of dogs), mirroring Haruna Sairenji's fear of the supernatural. This phobia frequently triggers uncontrollable bursts of her psychokinetic abilities, resulting in chaotic and often risqué accidents. Despite good intentions, she can be somewhat oblivious, misinterpreting situations or veering off-topic. She actively supports Haruna's romantic feelings for Rito Yuuki, frequently using her powers to encourage Haruna's confession—though these attempts typically backfire.

Her ghost physiology grants her abilities. In spiritual form, she flies, becomes intangible, and phases through solids. She possesses extrasensory perception, detecting auras, spirits, or energy fluctuations from great distances. A core power is possession: entering others' bodies allows control over their movements and access to their memories and emotions, though prolonged possession risks permanent soul fusion with the host. She also wields concentrated psychokinesis, moving objects, creating force fields, generating shockwaves, and performing exorcisms. This power can manifest as psycho-pyrokinesis, channeling spiritual energy to ignite targets. Panic—especially around dogs—causes her powers to spiral out of control, often leading to poltergeist activity, accidental disrobing, or suggestive entanglements.

Her development involves gradual integration into human society. After gaining her prosthetic body, she enrolls at Sainan High School, starting in Class 1-A before advancing to 2-A. She works as Mikado's nurse-in-training, though occasional clumsiness causes mishaps. Within *To Love-Ru Darkness*, she attempts to uncover the truth about Mea Kurosaki by possessing her, nearly resulting in Oshizu's absorption by Mea's inner darkness. Throughout the series, she remains part of Rito's social circle, frequently enabling or complicating romantic entanglements through her powers.

Key relationships include loyalty to Mikado as her creator and employer; friendship with Haruna, whom she helps navigate feelings for Rito despite Haruna's initial fear of ghosts; and a supportive but accident-prone dynamic with Rito. She appears in spin-offs like *Mayoi Neko Overrun!* as a background customer. Her name "Murasame" translates to "village rain" (a passing shower), while "Shizu" means "quiet." A trivia note references her dressed as Enma Ai from *Hell Girl* in one chapter, nodding to their shared voice actress.