"If you really want to fulfill your dreams, don't be scared to reach for it. You will really be a loser if you don't even try."

- Ritsuko Sakakibara

Ritsuko Sakakibara (榊原 理津子, Sakakibara Ritsuko) is the older sister of Reiko Mikami, the deceased wife of Yōsuke Sakakibara, and the mother of Kōichi Sakakibara, who only appears in the school graduation album and the old Sakakibara family pictures. She went to Yomiyama North Middle School in 1972 and was in the same class as the dead Misaki Yomiyama, 9th Grade Class 3-3.

Yōsuke Sakakibara mentions that Ritsuko is a very special lady who has a great taste in men and is also a supportive sister. Reiko Mikami mentions that when Ryōhei Mikami (Reiko's father) went against Reiko's decision to attend art university, Ritsuko was the only one who stood up for her and supported her. Also, in the manga, in Another 0 chapters, Ritsuko is shown as a kind-hearted, calm, and peaceful woman as she says that she will protect her younger sister after Reiko yelled at her. Reiko claimed that she admired Ritsuko the most, and she was her idol. Also, she was very happy when Ritsuko came to Yomiyama to give birth to Kōichi Sakakibara. Ritsuko was shown to be a loving and caring person.

.]] Ritsuko has long brown hair and brown eyes (black eyes in the manga). In her middle school days, she wears a ponytail in the anime, whereas in the manga, her hair is shoulder-length and worn down. Also, she is seen after Kōichi Sakakibara's birth in the manga, wearing her hair tied in a pigtail.

In the manga, Ritsuko appears in Reiko Mikami's flashback. After Kōichi Sakakibara comes to live with Reiko, she is seen standing in front of Ritsuko's altar, talking to her. In Chapter 10, it is hinted that her death was in that class because of the calamity. And it was also confirmed that she is actually The Death Of May of the 9th Grade Class 3-3 in 1983. In Another 0 chapters, it is shown that she died shortly after Kōichi's birth. Misaki Yomiyama enters the room, Ritsuko calls his name, and then dies. The cause of her death is unrevealed. After her death, her father (Kōichi's grandfather) is always seen sitting in front of her altar, probably still depressed about her death, claiming that he is sick of funerals (including Reiko's). Also, Rei (the family's pet bird) always repeats the phrase "Poor Ritsuko, poor Reiko". In Episode 5, when Kōichi was looking at his mother's class picture, the librarian, Tatsuji Chibiki, came to him and asked about his mother. Tatsuji is shown to know about his mother since he was the homeroom teacher of class 3-3 in 1972. In Episode 10, Kōichi showed Mei Misaki some old pictures of Ritsuko in her teens.