Kogetsu Takamatsu acts as the chairman of Yurigaoka Girls' Academy, an institution training Lilies to combat the Huge threat. He is the younger brother of Takamatsu Shiera. Both siblings fought in humanity's early major conflict against the Huge, the historic Antarctic Campaign. This battle predates the service of any Lily active in 2052 and ended in catastrophic defeat following the death of key warrior Anja Herzog. Less than 10% of participants survived; Kogetsu and Shiera were among these few survivors, later hailed as "heroes of Antarctica." The campaign was notable for including male combatants alongside Lilies, a rarity in the war.

After the Antarctic Campaign, Kogetsu took on administrative duties at Yurigaoka. His responsibilities encompass overseeing academy security and liaising with external committees like the Security Inspection Committee. He displayed vigilance toward external threats, questioning the committee's motives regarding an unnamed girl discovered near Huge remains on a beach. During such investigations, he collaborates closely with staff members such as Shinobu Izue.

Kogetsu approaches anomalies in Lily capabilities methodically. He personally administered a Magie ring test to a male candidate showing rare synchronization with a Charm, seeking verification of Magie energy presence, reflecting his role in evaluating potential Lilies under unconventional circumstances. His leadership extends to crisis management involving unexplained individuals, including authorizing the rehabilitation of amnesiac girl Yuri Hitotsuyanagi while maintaining institutional oversight.