Mirai Kimizuki

Mirai Kimizuki 「君月 未来, Kimizuki Mirai」 is the younger sister of Shihō Kimizuki. She was infected with the Apocalypse Virus despite being a child and is being treated in a hospital. Shihō joined the Japanese Imperial Demon Army in order to gain access to the military resources that are needed to cure her as the virus cannot be treated in civilian hospitals.

History
She was one of the children that was being experimented on by the Hyakuya Sect to create a weapon of mass destruction, as part of the 'Seraph of the End' plan in destroying the world. Guren knew of this beforehand, thanks to intel provided by Mahiru eight years ago.

She got infected with the Apocalypse Virus despite being younger than thirteen. Kimizuki took care of her, even though they lived in the outside world with monsters. She wanted Kimizuki to kill her, but he refused and they eventually entered Shibuya. By joining the army, Shihō got the resources and money needed for her care.

Trivia

 * Mirai 「未来」 means "future."
 * Kimizuki 「君月」 means "your moon."
 * Despite being younger than 13, she was infected by the same virus that killed those 13 and older during the Apocalypse. Kimizuki took care of her until he entered the safety of the JIDA.
 * In the light novels, it is confirmed she and her brother are also results of the "Seraph of the End" experiments the Hyakuya sect undertook.
 * Even though she is shown covered in ofuda in the manga, the ofuda do not appear in the anime.