Naisho no Tsubomi is a critically acclaimed manga that tells the story of Tsubomi Tachibana, a fifth grader dealing with rather sensitive issues such as her mother's pregnancy, her first period and the strange feelings she has started to get when around boys. When she first met Daiki, she tends to blush a lot when she is around him, she does not know what that feeling is at first, but further into the story she then discovers that she, in fact, has fallen in love with Daiki.
Each volume tells the story of a different girl, always with the given name of Tsubomi and similar appearance. In each case the story deals with various issues the girl experiences with early adolescence, including physical matters such as menstruation and breast development, personal issues such as the first crush, and more uncommon but dangerous issues such as the risk of predation (this was not included in the anime). Each story also includes some source of candid advice and information to support the girl, such as the spirit of a future sibling (volume 1), an alien posing as a twin brother (volume 2), or even another self from a parallel universe (volume 5).
A fifth grader who deals with sensitive issues while growing up. She is worried about the people around her and tries hard to help them when they are in need. This leads to her trying to handle issues such as her first menstruation alone. Although Tsubomi is a responsible and helpful girl, she is naive in a sense that she does not understand many things around her. She is happy about her mother's pregnancy.
She is troubled about lot of things like the strange feelings that she has around Nemoto, the "indecent things" that her parents have done to make a baby, and her feelings towards Saya when she gets close to Nemoto. Tsubomi is shown to have feelings for Nemoto but does not quite know it herself at first. She later confesses to Nemoto, and the two become a couple.
A beautiful new transfer student in Tsubomi's school and class. She knows many things and is a friendly character. She gets along with Tsubomi from the beginning of the story and acts like a sister to her by helping her with her problems. Not only she helps Tsubomi, she even helps Daiki. She seems more mature than other children of the same age.
He is friend of Futoshi and You. He calms Tsubomi down when she is going to see her mother and gives her a toy duck which she to attaches to her bag. He is nice and popular with girls, including those who are older than himself. He starts to have feelings for Tsubomi, and realizes them after they secretly see Yae and Yō kissing. Later in the series, Tsubomi confesses to Nemoto. He returns those feelings with his own, and the two become a couple.
She is tall, slim and calm. She is one of Tsubomi's best friends and her nickname is "Yae-chin". She is troubled by buying bras and her flat chest. She likes Saegusa and starts going out with him in chapter 5, and they kiss in chapter 9.
She is small, hyperactive and very curious, mostly about perverted things. She is one of Tsubomi's friends and Futoshi's childhood friend. She is teased by Futoshi many times, which makes her want to be slim and beautiful. Her nick name is "Rea-Pi".
He is quiet, very popular and considered "the class idol". He has an older sister that helps Yae with her problems. He likes Yae and becomes her boyfriend in chapter 5, but they keep it a secret because many girls would be jealous.