Sui's older sister, Sanae Kaburagi, was one of the Fafner Titan Model pilots who died while participating in the L-Plan. His parents Mitsuru Kaburagi and Kanae Kaburagi were deeply traumatized because of their daughter's death, and their relationship to Sui thus suffered. He constantly felt as if he was worthless to his late sister, while his mother became obsessive over Sanae's sacrifice and attempted several times to propose another L-Plan to Fumihiko Makabe.
