Morgana

Morgana is the cursed, sharp-tongued witch living in the mansion. Her presence is unknown, and she is one of the mysteries surrounding the tale. Morgana is presumably named after Morgan le Fay.

[Spoiler] The victim of unimaginable torture at the hands of the lord. She prefers to keep her face hidden so people can’t see the strange marks that cover it. Morgana is a doggedly aloof young girl who rarely acts her age. [/Spoiler]

(Source: Visual Novel Database)

[Spoiler] Near her death, Morgana's spirit splits in two at the Observation Tower—one half embodying her hatred and despair, while the other retains the purity and kindness of her earlier self. After Morgana's death and her legacy as a witch begins, the mansion is eventually purchased by the Bollinger family. Their youngest son, Michel, comes to live there, unknowingly awakening Morgana's lingering spirit. Initially manipulated by Morgana, who uses his traumatic past to isolate him, Michel gradually changes thanks to Giselle's presence.

Meanwhile, Morgana's separated "pure" spirit, wandering the mansion in the form of dust, silently observes Michel. Deeply moved by his selflessness and his bond with Giselle, she comes to idolize him. As a result, when manifesting again in human form, she adopts his name and appearance—becoming Michelle, the White-Haired Girl. Through this form, she plays out the tragedies of the first three doors, not out of malice, but as part of the mansion’s repeating cycle. [/Spoiler]