Nanami Shinonome begins as a human student who serves as student council president at the school that becomes the site of the Vampire Bund. She holds a stern, no-nonsense demeanor and initially opposes the idea of vampires attending the school, viewing them all as evil. Her background is that of a dedicated human student with a strong sense of order and a distrust of the supernatural. Nanami's personality is marked by a rigid, principled exterior and a hidden vulnerability. Her motivations are largely driven by her deep, secret feelings for Yuzuru, her next-door neighbor, and later by her struggle to control the powerful emotions that come with vampirism.

Her role in the story shifts dramatically after she is attacked by vampires one night while staying late at school. She is forcibly turned into a vampire and comes under the influence of enemy vampires through the master-servant bond inherent in the transformation. She initially serves the opposition even after her master's death, acting under duress because her secret love for Yuzuru is used as leverage against her. As a new vampire, she finds herself unable to control her heightened lust, leading to a violent and traumatic encounter where she nearly assaults Yuzuru. This event forces a confrontation between them.

Nanami's key relationship is with Yuzuru, the young boy she has loved secretly. Their bond is central to her arc: after being overwhelmed by her vampire instincts, she is confronted by Yuzuru, who admits he loves her in return. He willingly allows himself to be turned into a vampire by her so they can live together in the Bund. Her development moves from a prejudiced human student to a struggling new vampire who must learn to manage her intense new emotions, and finally to a reconciled person who reclaims her role as student council president. In supplementary material, she is also shown to have become one of Mina's maids, indicating a full integration into the vampire court.

As a vampire, Nanami gains the standard abilities of those turned in this setting: enhanced physical strength, speed, and regenerative capabilities, along with the potent emotional amplification that makes vampires prone to violent and sexual urges. She is noted for having a very keen eye for detail, a talent she retains from her human life. Her initial inability to control her vampiric hunger and lust defines her early struggle, and her character development centers on learning to manage these powers alongside her restored humanity.