From the moment you encounter Minatsu, she makes it clear that there are two things she hates: humans, and bananas. Of course, that's very important to the plot going forward, as Minatsu's story essentially revolves around breaking down that barrier of hatred and mistrust.
From the get-go, she seems to take a special exception to Yoshiyuki, as he and Suginami woke her from her... well, robot sleep chamber. Dr. Mizukoshi, one of the chief scientists charged with Minatsu, asks you both to keep her true identity a secret as the now-awoken Minatsu makes her debut as a transfer student in Kazami Junior High. When Yume introduces her new classmate to you at lunch one day, she's a bit surprised to see that you two seem to already know each other; it didn't help ease her suspicions when you both got singled out over the intercom to come to the Nurse's Office. Dr. Mizukoshi asks you (not unlike for Miharu in D.C., of course) to look out for Minatsu at school, since you know her secret. Your encounters with her often involve quick-thinking to find a banana-related product (keep in mind, she "hates" bananas) when her "bananamin" warning alarm goes off ("bananamin" is one of her power sources).
In addition to you and Yume, Minatsu also becomes friends with Anzu. So, between you and Anzu, Minatsu starts becoming a part of the core group of friends in Yoshiyuki's class, and gets invited on the Ski Trip. Minatsu has never skied before, but takes it on everyone's word that it'll be a lot of fun. On the trip itself, she proceeds to blitz past everyone on her first run down the hill, much to Yoshiyuki's surprise. In spite of having "never skied before", she did take the opportunity to read the manual and practice using simulations. The advantages of being a robot.
As the trip was winding down to a close, Minatsu and Yoshiyuki decide to go on one last run down the hill when the weather turns sour. Of course, they're able to find a cabin up the hill, and decide to weather out the storm. When Minatsu's bananamin warning alarm goes off, he's lucky to have a banana-related product on him... but later she starts wheezing uncontrollably, and she asks (with much embarrassment) Yoshiyuki to wind her spring using the spring-hole in her back. In true Miharu-fashion, this is accompanied by the requisite suggestive moans and groans... and in true cliché fashion, that happens to be just when Nanaka and Wataru happen to find them.
As they arrive home from the trip and prepare to head their separate ways, the group finds Minatsu wheezing uncontrollably, so Yoshiyuki has them all come and bring Minatsu to his house. At this point, the secret's out: Minatsu's not human. Once Minatsu regains her strength, she reveals her true nature to the group (who were all waiting at Yoshiyuki's house for news), and apologizes for having kept it a secret. Yoshiyuki's worried about what will happen now that the secret's out, but Wataru's offended that Yoshiyuki would place so little trust in his friends. They all assure Minatsu that she's their friend, robot or not, and that this won't change that at all, which moves Minatsu to the point of tears.
As the third "act", and winter school term, begin, Minatsu and Yoshiyuki continue to get closer. One evening, Yoshiyuki helps her out once again, and as a sign of her thanks and friendship, she begins addressing him by his first name. This takes him aback a bit at first, but he reciprocates by calling her just "Minatsu". None are taken more aback by this, though, than the prim-and-proper Yume, who has a hard enough time coming to grips with not addressing your senior students with "-senpai". Minatsu also meets Yoshiyuki on the road to school in the morning, and waits for him by the shoe lockers at the end of the day; it's starting to get pretty clear to everyone that Yoshiyuki and Minatsu are getting pretty close.
One day on the way home from school, Minatsu starts reflecting on her friendships, and concludes that her blanket hatred of humans was wrong. She realizes that her meeting Yoshiyuki wasn't a coincidence, and wonders why he stayed so close by her despite all their misunderstandings. Of course, he answers that it's because he's in love with her. She's not sure at all how to respond (when Yoshiyuki suggests "I'm so happy! I love you too!" she's particularly shocked.
), but says she'll answer him the next day. The next day, she appears at Sakura's house, where Otome and Yume are joining Yoshiyuki for a meal. When Yume comments that it's unusual that she'd show up, she notes (rather matter-of-factly) that it's not unusual at all, given the nature of their mutual relationship since yesterday. Of course, this nearly sends Yume into shock, much to Minatsu's confusion, and he proceeds to take Minatsu and bolt out of there as quickly as possible.
Later, by the school, she opens up to Yoshiyuki and shows him notes she's been writing about plans for robots taking over the world. This is how she had built up a rapport with Anzu, who's a bit of a storywriter herself. Of course, this isn't just a story, really; it's a culmination of her inner thoughts and dreams and a way of directing her "hatred" towards humans. But she hasn't shown Anzu the latest page; now, instead of world domination, she wants to discover a new world where humans and robots can get along, with Yoshiyuki by her side. So, of course, her answer is yes. When Yoshiyuki gets home, faced with the to-be-expected grilling by Yume and Otome, he admits that he loves Minatsu. Otome isn't sure "whether to be happy or worried"...
Meanwhile, rumours about Minatsu around the school are beginning to grow out of control. Among the most uneasy is Yoshiyuki's class-rep Maya, who seems to have a real bone to pick with Minatsu and robots in general. While Yoshiyuki and friends do their best to show their friendship, life's starting to get uneasy for Minatsu. Meanwhile, she keeps brushing it off; in a confrontation with Maya, she's pretty cordial until Maya tries to drag Yoshiyuki into it. We find out that Maya's hatred towards Minatsu isn't actually about Minatsu herself, but rather a long-held grudge against robots in general, who she blames for her father's death (he was a scientist who worked on the "Myu" robot project). Maya's petitioning to the student council to have Minatsu kicked out of the school, since it's a school for humans, and not for robots. The student council doesn't seem to agree with her, though, a fact Maya bitterly attributes to Yoshiyuki's close personal ties to Student Council president Otome.
The next day, Yume bolts into the classroom with big news about Minatsu - Yoshiyuki and Maya run to the school entrance only to discover Maya's little brother crying in shock. He came to school to bring Maya her lunch, and was saved from an accident by Minatsu, who's now in hospital. Yoshiyuki rushes to the hospital; a few tests are pending, but thankfully Minatsu seems fine ("I'm a robot, after all.") Yoshiyuki takes advantage of the opportunity to ask Dr. Mizukoshi if she knew Dr. Sawai (class-rep Maya's dad), which she did. I'm not sure I caught the entire resulting conversation, but my impression was that Dr. Sawai was incredibly dedicated to his work, and saw Myu as a daughter of sorts - perhaps overshadowing his own family and his health as a result (hence why Maya blames robots for her father's death). Later that evening, Maya and her younger brother go to the hospital to thank Minatsu for saving his life; was Maya wrong about Minatsu and robots all along?
The next day, Yume bolts into the classroom again with more big news about Minatsu: it seems she's being expelled from school! Ever since the incident, she's been the talk of the school, and is widely seen as a hero for saving the boy's life. But her true identity as a robot can't be dismissed as a rumour any longer, which is causing some apprehension, so the school felt they had to act. Dr. Mizukoshi and Mayuki (Otome's friend and Student Council Vice-President) realize that nothing can be done. Upon hearing the news, Yoshiyuki's group of friends are all saddened and upset, but the most upset of all is Maya, who proceeds to organize a spontaneous protest! While she had been blaming robots for the death of her father, Minatsu put her own life on the line to save Maya's precious family. (Maybe humans and robots can co-exist after all?)
As Maya helps fuel anger throughout the school, Minatsu begins to get troubled over the uproar being caused for her sake. She asks Yoshiyuki what she should do, and he suggests that she should tell everyone her feelings. So, she decides to enlist the help of Nanaka and Suginami to address the whole school over the intercom. She thanks everyone for their support and concern, saying that it makes her very happy. But she accepts her fate, and asks everyone else to do the same. In return, she makes one request: that everyone should enjoy their school life as much as possible each and every day.
The next day, Yoshiyuki, Minatsu, Maya and the whole gang go out after school for some fun on the town (and discover that the uptight Maya's actually a good karaoke singer?!
), and Minatsu gives her tearful, heartfelt thanks to everyone. But Maya and Koko promise her one last farewell: Minatsu's Graduation Party! The next day, Yoshiyuki and Minatsu go on a tour of the school in an attempt to find everyone, reliving all the memories that brought them together over the last weeks. Finally, they get a call from Koko to go meet everyone waiting in the gym. When they open the doors, Minatsu finds all of Yume and Yoshiyuki's classes there cheering her arrival, as they ask her to come forward to receive her graduation certificate. With eyes full of tears, she thanks everyone. (Cue Minatsu's credits)
(Spring, one year later...)
Yume, donning a high school uniform, walks with Yoshiyuki to school as they begin their new school year. As Yoshiyuki settles into class, Yume bolts in with "Big News!" They run out and find Minatsu, in high school uniform, introducing herself as a robot and Yume's classmate. "Tadaima, Yoshiyuki..." (Cue "Spring Has Come") It seems the world where humans and robots can co-exist as equals is here.
...Oh yeah... I never mentioned how the hatred of bananas plays into it. Umm... suffice it to say that in her relationship with Yoshiyuki she, err... discovers the most delicious "bananamin" of all...
