- — Fornax and Segin, chapter 3.
Segin (セギン Segin) is a native of Lampetia and a primary antagonist in Heirloom Star. Despite possessing magic manufactured by the Cirque du Peur and working for the same faction, Segin is not a formal member of the team, instead Corona Austrina's adoptive child serving as Aganju Castle's caretaker and making daily rounds in the Tomb of the Stars, where the Cirque du Peur's bodies are petrified.
The novel is largely nondescript in terms of Segin's appearance, due to a constantly-worn dark blue hooded cloak obscuring Segin's face and body.
Segin first appears in the second chapter while making nightly rounds in Aganju Castle, noticing in the process that Fornax, who was previously healing her injuries through petrification, has been replenished and is no longer in the castle. Chapter three shows Segin waiting in the Tomb of the Stars to see if any other constellations will reawaken as well, but things stay the same. Fornax abruptly returns and Segin becomes annoyed with her hyperactivity and airheadedness, but learns through her that she found Lepus and Yumemi, a girl who possesses her power. She makes her uncertainty known to Segin, since a human being born with a constellation's power is virtually unheard of, and is worried that other constellation clans will use Yumemi's power for their benefit. Without warning, Segin leaves the castle, for reasons Fornax assumes to be related to investigating Earth being property owned by Corona Austrina or to stop other clans from reaching Yumemi.
Segin is the name of Epsilon Cassiopeiae and Gamma Boötis, two stars in the Cassiopeia and Boötes constellations, respectfully.