Sumi is in love with Mitsuru, but he doesn't seem to be interested in her as a woman. Determined to look more sexy and mature, Sumi takes an experimental growth hormone that her scientist father has been developing. However, the medicine backfires. Instead of changing into a buxom femme fatale, Sumi changes into a beautiful young man! She--he--is so gorgeous and so cool that even Mitsuru begins to take notice. Although the new situation with Mitsuru is imperfect, Sumi discovers that she can be closer to her crush: they can talk man-to-man. Yet, being Mitsuru's friend also has a downside, particularly when he reveals that he is in love with a girl in his grade!

Yuuki Ashikaga is a high-school freshman at Sakakino Academy. While working as a student librarian, he grows enamored of Kotonoha Katsura, a girl who frequents the library. Unfortunately, Kotonoha is already dating Makoto Itou, another schoolmate.

The situation is further complicated when Chie, Yuuki's older sister introduces him to Roka Kitsuregawa, her kouhai in the basketball club. Roka becomes interested in Yuuki, who only has eyes for Kotonoha. In order to make him jealous, Roka lies and claims she already has a boyfriend, her former classmate Makoto Itou. Unfortunately for all of them, Roka's lie sets off a chain of events no one could have predicted...

Note: Cross Days takes place in the middle of the original School Days storyline and provides an alternate take on how things might have turned out.

From Intercross:

For all of Mao's life, she has longed to be girly and have tea parties with beautiful girlfriends. And finally, she has that dream right in her reach, until she walks in on three boys changing at her private all girls school... What's a girl to do when another girl she admired turns out to be a guy?!

From Shoujo Crusade:

Karin HATES guys. She can't stand the sight of them, let alone be near them. But after a near death experience she finds herself waking up to a guy she doesn't know, within a guy school and in a guy's body!!?!

Jeong-Hwan received a letter from his sister Ji-Yeong that said, "Please rescue me, the devil is here!"

His sister goes to an all-girls school and in order to rescue her, he must disguise himself as a female student. In this school, all students are candidates to become "the bride of the devil."

Just before entering the university, Yanagiba Masahiko's father died in a car accident. His mother died when he was four, which makes him now really an orphan. But even before the death of his father, he didn't have a family life, as his father was always busy or abroad.

When his mother's younger brother and his wife decide to invite him to live with their family, his life takes a turn. But it is not going to be the normal family life he is imagining for himself. What is the "terrible" secret that led his parents to break the bonds with his aunt and uncle? What could be the true nature of his cousin, Shion? And last but not least, will this "terrible" secret eventually get Yanagiba, too?

Becoming part of a family...

Bohm (meaning spring in Korean), on his way to give his dad, Detective Ghim, (who's been working for 10 days straight) some underpants at the police station, sees a girl by a vending machine and wishes to see her again...

Mahnsoo, a boy with a strange lonely past, the only witness to an important criminal case, must undergo a disguise as a girl and stay together with Detective Ghim's family until the investigation is over and the case ends. So he meets Bohm again, and trying to get close to his new icy brother is not easy...

From Wikipedia:

Shimeru Futaba is a normal high schooler living a normal life, active in his school's wrestling club and slowly getting closer to his awkward love interest, Misaki. This fails to last, as he discovers his family's hereditary genetic defect that becomes active at adolescence. Although it will eventually become controllable, excitement and stress now make Futaba switch sex. Hilarity ensues.

From Viz:
Miaka Yuuki is an ordinary junior-high student who is suddenly whisked away into the world of a book, "The Universe of th Four Gods". There she becomes the priestess of the god Suzaku, and is charged with finding all seven of her Celestial-Warrior protectors.

A Japanese student named Arisu gets on the wrong bus and winds up in some sort of homoerotic version of Lewis Carroll's Wonderland. The last thing you want to do in a land where people change shapes at the drop of a hat is to drop the soap and introduce yourself as Arisu (identical in Japanese to Alice), lest you start looking like one! And Arisu does, slowly but surely...

From Ivyscan:

Karin and Lisette are witches who trained together when they were younger. After a long absence, Lisette has moved to a nearby forest and seems to be stealing Karin’s customers. Karin really wants to see her old friend again, but she can’t seem to get past Lisette’s apprentice, a young man named Ruin…

Volume 1 Oneshot: Meeting Place
About a student that can't say thanks to her overly enthusiastic teacher; so, she is thrown back in time to figure out that she still can.

Volume 2 Oneshot: Mission Sachiyama
About an after school program that trains modern day ninjas.

Reiji and Kasuga head out to Tokyo to become the "Gods of Rock," but they seem to always attract trouble. On their way, Hayama Ryo and Fujii Ran join them in their quest.

From Wataame Shoujo:

The story is about Kobato going to Japan to find her brother but accidentally, she becomes an idol when she meets Takeru. The catch is, Takeru and probably everyone else thought she was actually a he because of how she acts and dresses.

A very short story (3 pages long) about a boy who transform into a girl to become a hero, but she has to collect stamps to be a real hero.

Yona Ryouma, a normal high school boy, saves a man from another world at the cost of his own life when a mysterious earthquake occurs. The man, Emillio, uses a potion which apparently saves Ryouma's life. However, he is also changed into a girl in the process.

Emillio is actually the prince of this alternate world and he declares Ryouma as his wife, presumably on the context of saving his life. But what about Ryouma's life as a high school boy in his own world? And will he come to accept being the prince's wife?

Yukinari Takase is a huge masochist who instantly takes a liking to Rion Tachibana, a menacing trap who just transferred into his class. After Rion believes Takase has uncovered his secret, he decides to make Takase his servant in order to keep his mouth shut.

Note: Because Shinjo Mayu stopped her job relationship with Shogakukan, she continued her incomplete manga in Asuka and called it Ai Ore! - Danshikou no Hime to Joshikou no Ouji This can be considered a continuation of Ai (w)o Utau Yori Ore ni Oborero! or even as a second series.

In this screwball romantic comedy, Haruhi, a poor girl at a rich kids' school, is forced to repay an $80,000 debt by working for the school's swankiest, all-male club--as a boy! There, she discovers just how wealthy the six members are and how different the rich are from everybody else...

Includes 4 chapters of the story "Romantic Egoist" in various volumes, starring a pair of twins who play matchmaker with their fellow students, teachers and the like.

This is a 4-koma comedy about a young girl named Ichimatsu Kohina who got possessed by a low grade spirit called Kokkuri-san.

Masago is an average student. Everything about her is average except for her older brother, Shirou. He's the president of the student council and everyone admires him. One day, while walking home with her brother, they get into an accident and her brother dies saving her. After Shirou's funeral, Masago goes to the house of her brother's best friend, claiming to be her older brother.