Inamori Mayu

Birthdate June 11, 1992 (Heisei Year 4)

Computer says she's 16 (at the time of disappearance), but with a birthdate on 1992, that would make her 21 years old. Continuity error.

Father's name is Shinji 真治 (45 years old)

Mother's name is Sayuri 紗由里 (40 years old)

Both parents are reported as missing.

History

Mayu first appears in a school uniform on her way to school. Nitou encounters her and assumes she is Medusa in disguise.

Revealed to be the twin younger sister of the Gate who spawned Phantom Medusa.

Diagrama to show how Misa and Mayu's names come from their parents

Nakayama Erina plays both Medusa/Misa and Mayu.
Rinko finds Misa's profile on her computer. It reveals that her birthdate is June 11, 1992 (Heisei Year 4). Her real full name is Inamori Misa (稲森美紗).
- The interesting thing is that the computer says that she was 16 at the time (the age of the actual actress), but her birthdate was in 1992, so she would have to be 21 years old today. If they want her to be 16, she should have been born in 96-97 (Heisei 8-9).
- Father's name was Shinji 真治 (45 years old) and mother was Sayuri 紗由里 (40 years old), they're both noted as being missing.
- The big reveal of the episode 26 is that Misa has a twin little sister named Inamori Mayu. They drop a clue for this beforehand with Mayu's figure on her bag, which displays a four member family, two parents and two sisters.
- Misa and Mayu both take parts of their name from their parents Shinji and Sayuri.
- Misa means "beautiful gossamer" while Mayu means "true reason". Misa tends to wear a fine shawl, so it makes sense.
Either Misa or Mayu appears briefly in the opening of Wizard from the very beginning of the series, before Medusa's past is revealed.
Ignoring the kanji, Mayu is the Japanese word for "cocoon".