Sairenji Natsumi

Sairenji Natsumi is the mother of Sairenji Haruna and Sairenji Akiho.

Plot
She's mentioned first time in chapter 146 where Haruna narrates used her father to live together with the family but, during middle school, had to leave due to work and her mother joined him.

She made his debut in chapter 54 of Darkness, where her appearance and her name are revealed along with his wife for the first time.

Etymology

 * Sairenji means "west" (西) (sai), "link, take along, lead, join, connect, party, gang, clique" (连) (ren) and "temple" (寺) (ji), which literally means "The Western Continuous Garden" altogether.
 * Natsumi means "summer" (夏) (natsu) and "beautiful" (美) (mi).
 * With the debut of Haruna's parents in the Darkness Chapter 54, the whole Sairenji family will make up the four seasons of a year, thus completing the cycle:
 * Haru in Haruna is of Spring
 * Natsu in Natsumi is of Summer
 * Aki in Akiho is of Autumn (Fall)
 * Fuyu in Fuyuhiko is of Winter