Nami

She is the twin sister of Naomi, adopted into a different family following some tragedy. In most routes, she is the antagonists' target.

In the Mother & Father Ending, she is possessed by her mother's spirit and temporarily turned into a mummy.
In the Shadows Ending, her "shadow" is revealed as the source of the supernatural attacks in the mansion, using Nami's psychic powers.
In the Monster Bloodlines Ending, she is revealed as a vampire, unconsciously luring Kouhei into her father's trap.
In the Epilogues, its revealed all of the routes were tests set up by her family to prove Kouhei's feelings for her.