During the Sengoku period, the Ii family governs the Totomi region. Due to many past wars, there are no more male successors left to become a lord. Naotora Ii (Kou Shibasaki), the only daughter of the lord, now becomes a lord. She faces a difficult period. The constant love from her fiance, whom she became engaged with at a young age, helps her to keep moving forward.
Set along the Shimanto River in Kochi Prefecture, Japan. "Osozaki no Himawari" depicts the lives of seven people who follow vague dreams, but live an ordinary life.
Jotaro Kodaira (Toma Ikuta) is about to turn 30-years-old. Jotaro has recently been laid off from work and around the same time his girlfriend of seven years dumps him. Jotaro then spots a website recruiting people for work in Koichi Prefecture in a regional revival cooperation.
Kahori Nikaido (Yoko Maki) is clinician sent to work in her hometown of Koichi Prefecture. On the way to there, Kahori meets Jotaro Kodaira.
Kotoha Ninomiya (Manami Higa) works in the general affairs department at a confectionery company. Suddenly, she receives an order to transfer to the public relations department. She has a hard time there. Making things worse, Kotoha Ninomiya learns that Atsushi Imagawa (Dai Watanabe), whom she holds secret feelings for, is about to marry another woman. They have been friends since they were young. Heart broken, she attends Atsushi’s wedding ceremony. At the ceremony, she is moved by Kumi Kuon’s (Kyoko Hasegawa) congratulatory speech. Kotoha Ninomiya is a legendary speech writer.
Yuzuko Nanakusa (Koyuki) was betrayed by her husband. She now raises her son and daughter as a single mom, in addition to working at a company. One day, the company she works for goes bankrupt suddenly. She loses her salary and savings. While not knowing what to do next, Yuzuko Nanakusa is contacted by attorney Shinichi Kakihara (Atsushi Ito). They went to the same high school together.
Shinichi Kakihara tells Yuzuko Nanakusa that there is a something more to her company's bankruptcy. To protect the life of her two children, she attempts to reveal a big evil.
Detective Kazuma Asano (Nobuaki Kaneko) faces times off from work due to a specific case. He then meets model Rena Kurusu (Yu Yamada), who possess a special vision ability. They then pair up to solve difficult cases together.
Sharaku Homonji (Yuji Oda) is the eldest son of a distinguished family who has studied crime for generations. The eldest son from the Homonji family has tested for an IQ of 246 for generations and Sharaku Homonji possess an IQ of 246.
Soko Wato (Tao Tsuchiya) is a detective. One day, she is assigned to the investigation section #1. Her job there is not to investigate crimes, but to escort Sharaku.
Shinichi Sakurai (Sadao Abe) is married to Kanako (Kyoko Fukada) and they have a daughter named Kaori (Mikuu Yamada). Both, Shinichi and Kanako received only a middle school level education. Even though they don't have much money, they are a happy family. At work though, Shinichi experiences effects of only having a middle school education.
One day, Shinichi sees Kaori’s poor score for a national test. He freaks out and decides to improve Kaori's education. Thus, 41-year-old Shinichi begins studying with Kaori and instructs her for the upcoming middle school entrance exam.
Mikuri Moriyama (Yui Aragaki) is 25 years old. She doesn't have a boyfriend and doesn't have a job even though she holds a graduate degree. Everyday, Mikuri Moriyama has a feeling that she is not needed. Her father, unable to see her suffering anymore, arranges for her to work as a housekeeper. Her employer is 36 year old Hiramasa Tsuzaki. He is single and works for a company. A series of events leads them to marry as a working condition.
Riko Shirono (Mikako Tabe) doesn't have any big expectations for a man in her life, but she works as a love simulation game planner. She receives a request for a new love game from app company TIMEIS. Soichiro Kurokawa (Issei Takahashi) is the CEO for the company. He is almost perfect, but he can't understand woman’s mind.
One day, Soichiro Kurokawa (Issei Takahashi), who likes his subordinate Momose, asks Riko to teach him about love techniques. Due to Riko Shirono’s help, Soichiro and Momose get close, but Riko finds herself becoming attracted to Soichiro Kurokawa.