A young, brillant student who is enrolled in homeschooling by her parents with teacher Makita Yousuke, Yuuna Tachibana harbors many wild, lust-filled fantasies that she longs to try with the mortified Makita. She appears to be a normal girl on the outside, but inside she is a sex-craving girl.
A average, yet intelligent student at her local middle school, Yuuna Tachibana has reached the end of her 3rd year at school and is beginning preparations for her High School Entry Exam, which will take place within several weeks. Wanting their daughter to have the best chance at scoring a perfect grade and to qualify for the best high school and college in Tokyo, they enlist the teacher in training Makita Yousuke, a college-aged man who is looking forward to getting the money from homeschooling Yuuna that can help pay off some of his expenses from college.
Yuuna Tachibana was created in 2008 by writer and manga artist Takeda Hiromitsu for the Tsundero H-manga. It is not known as to what inspired Takeda Hiromitsu to create Yunna.
Not much is known or revealed regarding the early years of Yuuna Tachibana's life in Tsundero. What is known is that she is a decent student that was held back one year due to a poor test and has a promising future in front of her should she find academic success in high school and into college. It is also revealed that she has a dark side to her mainly bright, cheerful personality, which manifests itself in the form of being obsessed with her sexuality and how she longs to have sex with anyone that she can snag with her charm.
We are first introduced to Yuuna Tachibana in a special full-color segment of the first chapter of Tsundero, in which she is shown having sex with her homeschool teacher Makita Yousuke as she performs a messy session of paizuri upon him with her large breasts while he teases her privates with his tongue. This strange, passionate session continues until Makita reaches his limit from her constant stimulation and unloads his fluids upon her breasts, much to her surprise and satisfaction. This concludes the special full-color segment of Chapter One and this begins the true story of how Yuuna and Makita came to be lovers shortly after meeting each other.
The story picks up with Makita Yousuke introducing himself and talking about himself as he is shown sitting at a table with the Tachibana family as he enjoys a cup of coffee. Sitting across from him at the table is the beautiful Yuuna Tachibana, the lone daughter of the Tachibana family that he has been entrusted to help study and prepare for her high school entrance exam that will be happening in several weeks that will also determine her eligibility for a prestigious college down the road. He notices her strong charm and sex appeal, and tries his best to ignore them since he was hired so that he could help her better herself for the upcoming entrance exam that she will be taking several months from now. Frowning, he glances down at her large breasts with slight interest, but deems them too big for his personal liking since he prefers women with average breasts. Smiling, Yuuna tells him to treat her kindly, gazing at him with her cheerful eyes as Yuuna's mother yells at Makita for spacing out, snapping him back to attention as he hastily replies "I'll be...looking forward to helping each other". This begins his time as her homeschool teacher, and they get to work on studying and improving her understanding of the subjects she has minor issues with so that she can have the best chance at passing her exam in several months.
Makita notices that Yuuna's overall grades are not too shabby compared to what her parents had indicated, and finds himself interacting with her socially more and more frequently in comparison to doing her classwork or studying for the exam as the days pass by. Enjoying how much fun that he is having being her teacher and impressed with how much her grades were improving, Makita makes his way towards her house later that week to help her with her latest batch of school work. When he arrives at her front door, he remembers that the date is the 30th of March, and that her tests and exams will be starting up at her school within two months. Feeling confident that his lessons and methods will help her pass all of her upcoming tests, Makita knocks on her front door and is quickly greeted by the cheerful Yuuna, who is eager to allow him inside to see her seductive outfit. Makita is blown away by just how hot she looks in her current outfit, and notices that she is not wearing a bra either, for her nipples can be seen through her revealing shirt. Trying not to become aroused, he hastily avoids making eye contact with her and rushes off towards her bedroom, telling her "We'll study...the stuff you are not that good at!" in a shaky voice as he goes to head up the stairs.
Once inside her bedroom, the stunned Makita tries to clear his mind of what he just saw downstairs by busying himself with preparing the work that he plans to help her with today. She enters the room and sits down at the table next to where he is standing, her revealing shirt allowing for his eyes to glance down at her cleavage as he tries to ignore the situation at hand and get back to helping Yuuna study. Trying to get out of this provocative situation, he suggests to her that they should wear some thick clothes due to how cold the room is, hoping that she will put something on that will cover her seductive outfit and get him out of this uneasy predicament. With a coy, somewhat amused expression on her face, Yuuna looks up at him and tells him that she is "hot", pulling the front of her shirt out enough to expose her right breast along with her erect nipple, much to the shock of Makita. Suffering a minor freakout regarding just how far she is trying to take this charade, he quickly turns around and staggers from the room, making his way downstairs towards the kitchen to make some tea as she sticks her tongue out at him.
Later in the day, the two of them are shown doing work together upon one on the assignments that Yuuna brought home from her classes earlier in the day, sitting next to each other as Makita tries his best to ignore her provocative advances upon him. As Yuuna goes to erase a mistake upon her paper, she "accidentally" knocks her small eraser off of the table, sending in down to the floor by her feet as Makita takes notice of her blunder. Trying to be a nice guy and figuring that so long as he closes his eyes, she wouldn't be able to pull any advances upon him, he gets down on his knees and begins patting around the floor in his attempt to find the lost eraser for her. Before he knows it, she grabs him tightly with her thighs and he soon finds his face mere inches from her underwear, a shocked expression on his face as she calls him a "perv", laughing to herself as he tries his best to ignore what he deems as her "teasing with her adulthood". Thus begins the first set of many advances that she makes upon him while they are studying together, with each and every new attempt slowly becoming more and more provocative as Makita struggles to keep his mind clear of any thought regarding her luscious body. Several days later, the situation escalates to critical mass when the weary Makita is offered a massage by Yuuna after they wrap up their studies for the day. He kindly refuses her offer, but the insistant Yuuna forces herself upon him and begins rubbing her breasts against his back while her hands make their way towards his zipper in her attempt to get him to have sex with her. Enraged from her non-stop advances upon him and at his limit of patience with her, he turns around and shoves her away, sending the stunned Yuuna crashing down hard onto her bedroom floor much to his shock. Standing up, Makita apologizes to her for his crude actions, and decides that with her exam approaching in several days, that it is time for him to stop helping her study for it. Much to the surprise of the stunned Yuuna, he grabs his coat and heads out the door for the last time, not to return.
The following day, Makita decides to return to her house in order to apologize to her for his rude actions and to see if she was not hurt from what he did to her in his momentary outburst of rage. He enters her house and makes his way up the stairs towards her bedroom, calling out her name as he tries to locate her so that he can set things right. Stopping at her door, he pauses for a minute, thinking over as to what he will say to her regarding the events of the previous day before saying "I'm coming in...", slowly opening the door into her bedroom. Makita is blown away when his eyes fall upon the startled form of Yuuna, who is in the process of putting on her old school swimming suit and has both of her large breasts hanging out from her outfit. Recovering from this sudden development, he turns around and slams the door behind him, shouting apologies to her as he begins to suffer a minor freakout regarding what he just witnessed. Much to his surprise, the door suddenly opens and with a firm tug, Yuuna pulls him into her bedroom so that they can talk about what just happened.
Still in shock from what he witnessed, the perplexed Makita is addressed by Yuuna regarding the elementary school swimsuit that she was putting on when he happened to walk in on her. She tells him that she forgives him by coming here, and thus decides to set her latest plan to engage him in wild sex into motion. Makita, still fighting the urge to stare at her voluptuous body that her old swimsuit clings tightly to, stammers that she should put some clothes on, for she might catch a cold by wearing such a revealing outfit in the frigid air-conditioned house. Before he knows it, she pushes him backwards, sending him crashing down to the floor as she lunges forward and throws herself upon his lap, pivoting so that she faces him as she leans forward enough so her breasts are mere inches from his shocked face. Realizing just how close he is to losing control of his sexual urges, Makita struggles to resist both her charms and massive breasts as she tells him that this is "payback" for yesterday and that she wishes to have sex with him. When he tries to protest, she pulls out a package from under the desk and holds it up to his face, a coy smile on her face as he realizes that she has his new porn DVD that he had ordered in the mail. The DVD in question is a special feature that has various flat-chested women in the same kind of school swimsuits as the one that Yuuna is currently wearing, which turns out to be the fetish that makes Makita lose control of himself. Pleased with herself that she can blackmail him into sleeping with her, Yuuna reveals to him how she got the key to his apartment from the local postman, going through all of his things while he was away in town several days ago. With him caught tightly in her trap and with him on the verge of losing total control of his strong sexual desires, Yuuna slowly moves in and gives him her first true, passionate kiss.
With that kiss, Makita loses total control of his wild sexual desires and decides to engage her in the wild, passionate sex that she has been pestering him into giving her for the past few weeks. He hugs her tightly with both arms and engages her in another passionate kiss, confessing his deep love for her as they sit together on the bedroom floor by her desk. Now fully aroused from kissing each other, they both agree that it is time to move to the bed so that they can both show each other just how much they truly love each other. Makita lays down on the mattress, hastily removing his clothes as Yuuna pulls down her swimsuit so that her massive breasts can hang out for him to play with. Before he knows it, she jumps into bed next to him and smothers his face with her breasts, allowing him to toy with them along with her sensitive nipples as he decides that he will give up his hatred for large breasts and change his overall feelings on them. After several minutes, she engages him in the messy paizuri session that was first mentioned in the first paragraph as he toys with both her clitoris and nipples. When she has finished, she positions her hips in front of his erect privates and asks for him to help her study her sexuality by sticking his junk inside. Carried away with his desire to have sex with her, he gladly obliges and thus slowly slides his privates inside of her.
For the next hour or so, they engage each other in rough, passionate sex together that helps Yuuna achieve multiple orgasms and ends when Makita reaches his final limit and releases his sperm inside of her. When they have finished, they clean up and head off on their separate ways, for her exam is tomorrow and he is no longer needed to help her study for it. Several days later, he is shown running up her stairs and into her room, asking her as to how she performed on her high school exam. She tells him that she has passed, holding up the folder that hold all of their notes as he sighs with relief that all of his work has helped her achieve her goal of passing the exam. To his horror, she tears apart the folder in her hands, letting the pieces fall down to the floor as he stares at her in shock, trying to comprehend why she did that as Yuuna tells him how the sex she had with him was "the greatest thing for me". She then grabs another piece of paper and shows it to him, the name of the school and the college that she was accepted into printed on the page as Makita recovers from her shredding the folder that he had given her. With a coy expression on her face, she tells him to "please treat her kindly, sensei." as with her free hand, she pulls out her shirt enough to expose her left breast to his eyes. With that, so ends Chapter One.
As of today, Yuuna Tachibana has yet to be featured in any media/products outside of the Tsundero manga.