Kirigaya Midori

Midori Kirigaya (桐ヶ谷翠, Kirigaya Midori) is the mother of Suguha Kirigaya, but adopted Kazuto Kirigaya. She is an extremely busy woman and leaves the two kids to care for themselves, only coming back to the house late in the night and leaving early in the morning.

Background
She adopted Kazuto in 2008, after her sister's death and kept it in secret until Kazuto discovered the erased documents in the National registry in 2018. She told Suguha the truth while Kazuto was trapped in SAO.