Rina Yaegashi/Story Plot

Hito Random arc
Throughout the Hito Random arc, Rina remains largely oblivious to Taichi switching personalities with his fellow StuCS members.

Kizu Random arc
Rina begins frequently teasing Taichi about his girl troubles throughout the Kizu Random arc. Due to being the person who wakes Taichi every morning, Rina is distressed to find her brother unable to wake up after his impulse to sleep is unleashed, though he later makes an excuse to prevent her from becoming suspicious. Rina also wisely advices her brother to never allow his emotions to get the better of him after he has a fight with Aoki.

Kako Random arc
During the Kako Random arc, No.2  possesses Rina in order to speak with Taichi, whom is extremely disturbed to find his own sister possessed but is relieved when No.2 quickly releases her. On New Year's Day, Rina witnesses Taichi and Inaba with children. Without knowing the truth behind the children, she texted Taichi a very angry message written in all katakana demanding he explain what's going on. Rina becomes increasingly frustrated that Taichi is spending more and more time with the Cultural Society and seems to be more secretive around her. She even threatens to disown him if he doesn't come home. She remains unaware of the phenomenon her brother faces.

Michi Random arc
Rina begins worrying for her brother's deteriorating mood and tries to cheer him up to no avail. She presents him with "True Love Chocolates" on Valentine's Day, hoping they would make him feel better.

Later, Taichi sits Rina down and explains how it was inappropriate for her to present her brother with supposedly "True Love Chocolates," but Rina innocently states she was only kidding before giving Taichi a playful peck on the cheek. Taichi is thrilled.

Nise Random arc
Rina informs her brother that she now has a boyfriend which catches Taichi by surprise. She then horrifies her brother by claiming that her boyfriend is a third year in high school and Taichi commands her to break up with him.

Yume Random arc
Rina returns home one day to find Fujishima with Taichi. Fujishima was attracted to Rina in a way that Taichi did not agree. Before Fujishima did anything, Taichi kicked her out of the house.

Asu Random I arc
Rina noticed that her brother ,Taichi, was acting strange and became very worried. She ended up talking to Nagse's mother, Reika, and they both started to share information on the strange behaviours of Iori and Taichi. Later they ended up deciding to go to Yamaboshi High School to see if the cause of the strange behaviour was bullying. When they got there, Rina felt strange as she approached the school. Rina and Reika talked with Gotou about Taichi and Iori and Gotou gave some advice to the two. He said to Reika and Rina,"You have to let the childeren fly away from the nest, but let them know that there will always be a place to return to." When Gotou's conversation with them was finished Rina and Reika met Chihiro and Shino and they gave her something to give to Taichi and Iori. After Gotou being posessed by Heartseed (original) talked with Rina and showed her everything that has happened with the StuCS. After understanding the hardship Taichi has gone through, Rina fainted and was taken to the Nurse's office. When she woke up, she called Taichi to come to the school to pick her up. Taichi called the rest of the StuCS as well. Taichi got there first and they both had a touching reunion in which the rest of the club members watched secretly. At the end of part 1, Rina discovered something in Taichi's school bag.