Rena Nakano

No matter how scary or stone-faced she was, she was forgiven. She was loved and adored. That's because sensei was such an incredibly beautiful woman. Rena Nakano is the late wife of Maruo Nakano and the biological mother of the Nakano Quintuplets who worked as a teacher before she had succumbed to an illness when her quintuplet daughters were just ten or eleven years old.

More of her history may be explored the movie via flashbacks.

Appearance
Rena has chest-length dark-colored hair (dark-red in the anime) that has bangs swept to the right side (she had shoulder-length hair that hangs on the right side when she was a high school student), light-colored or dark-colored eyes (dark-blue in the anime), a well-endowed figure with large breasts and full pink lips; traits (like her beautiful looks/figure etc.) that had been passed down to her daughters.

Her beauty has charmed every male/female student and Shimoda comments on Rena's looks to Itsuki Nakano in different versions:

According to Mudou in Chapter 109, he comments to Itsuki on how "you're the spitting image of your mother when she was young."
 * In Chapter 57 (Pg. 10-Pg. 12), she mentions "that's because Sensei was such... an incredibly beautiful woman."
 * In the English Sub, she comments on how "Sensei was just that damn super beautiful."
 * In the English Dub, she noted that "Ms. Nakano was just that stunningly beautiful."

Personality
Rena is known to be a very serious, unsociable, strict and stern woman, especially when it comes to teaching her students as she would often punish her students with iron-fist sanctions, but she was also very forgiving and for that (as well as her appearance), she was adored by her students that there was a student fan club dedicated to worship her.

According to Itsuki Nakano's words, Rena was "a gentle and maternal female."

Background
Rena was a single mother who raised five children. Before her remarriage with Maruo Nakano, she and the quintuplets were living in poverty like the Uesugi Family where it is implied that the biological father of the quintuplets abandoned her and the children, which is why she advised the quintuplets to be careful when choosing men.

She was a teacher at a high school where she was well-loved and respected by her students. Shimoda was once her student and was inspired by Rena to eventually work as a lecturer at a cram school.

She passed away five years prior to the start of the story on August 14 from an unknown terminal illness and her death was a shock to the quintuplets, whom she had constantly reassured that she would be fine. After her death, she is currently buried at the Nakano Family Grave where Itsuki Nakano mostly visits.

Season One

 * Day Off (debut; flashback cameo)
 * What's Been Built (flashback; cameo)

Season Two

 * Seven Goodbyes, Part 3 (flashbacks; cameos)
 * The Last Exam (flashback; cameo)
 * The Movie (final appearance; flashbacks)

Mr. Nakano
Her relationship with her father seemed to have been quite obscure, though her early death had hit him hard.

Mudou
Before Rena remarried Maruo Nakano, she was once married to this man who is the quintuplets' biological father. It is uncertain what exactly caused them to split up, but Itsuki Nakano states that he left after finding that Rena was pregnant with quintuplets. When she was alive, she advises the quintuplets to always be careful when choosing men, which shows Rena's regret for marrying this man.

Itsuki Nakano
Itsuki was definitely close to Rena as Itsuki goes to her mother's grave on the 14th of every month. Rena also acted as a role model for Itsuki, who listens to her words, especially when it came to choosing men. Due to this, Itsuki aspires to become a teacher just as her mother once was.

According to Mudou and Shimoda, they comment on how Itsuki strikingly resembles Rena.

Maruo Nakano
Maruo is Rena's new husband. Before getting married, Marou was one of her students who often visited her in the hospital when she became ill.

Shimoda
Shimoda is Rena's former student. Even as a delinquent, Shimoda admired Rena as a teacher and fell in love with her. Shimoda would later become a teacher just like Rena. After Rena had passed away, Shimoda would even go to her grave in order to pay her respects.

Trivia

 * The name Rena means "zero, nought" (零) (re) and "apple tree" (奈) (na).
 * The kanji "零" fits in with the numerically based names of her daughters.
 * The name of Toraiwa Hot Springs, the hot spring inn run by her father, is a pun toward Rena's personality. Tora (虎) literally means tiger, addressing the fierceness toward her students, and Iwa (岩) translates to rock, which can be interpreted as "hard to read."