From Intercross:

Kurosaki Mafuyu was a juvenile delinquent and head of her gang before her subsequent arrest got her expelled from high school. Now that she’s transferred to a new high school, she’s determined to become an “ultra-shiny, super feminine high-school student.” But with a new friend like Hayasaka-kun and a homeroom teacher like Saeki Takaomi (who may be more than he seems), will Mafuyu really be able to live a girly-girl high-school life!?

From Aerandria Scans:

It's the 16th century and the knights of the Mediterranean country Malta take pride in being the strongest in the world. Aciel is a beautiful lady-knight who gradually makes her way into the group of the knights, despite the fact it's forbidden for women to be knights. Learn the tale of the magnificent knights whose charms neither friends nor foes can resist!

From Condensation: Although Gyu Hwa Lee might look like a guy, she has feelings like any other girl. In fact, she's currently in love with Korean pop idol Kang Un Ryu. As luck would have it, Kang Un ends up transferring to Gyu Hwa's high school. The only problem is he has to keep his identity a secret so he's cross-dressing as a girl! What happens when Gyu Hwa discovers Kang Un's secret? Will she ever be able to win over his heart? Or will she always be nothing more than just a friend? A Korean manhwa with surprising poignance and refreshing humor by the author of Cynical Orange.

A boy's older brother gives him a potion that turns him into a flat-chested school girl.

What if the person you liked was the same gender? A beautiful girl suddenly appeared in front of the main character, Yuji! But what's her real identity...!? A new generation love comedy that questions “true love” in between tales of laughter and sadness.

Keito Azumi, an ordinary high school boy, was reincarnated as the heroine in a different world when he woke up in an accident! The worst thing about this is that his best friend became the hero!

Stories following various adolescent girls and their encounters with puberty and other worlds.

Marimo Himenogi desperately wants to become an idol singer. When a local contest is announced, she begs her boyfriend, Ayumi to sing as her partner. Ayumi relents, and disguises himself as a girl so that he and Marimo can enter the singing competition. Surprisingly, they win and are signed to a recording contract as a new group called "Twinkle". Now they must keep their newfound fans from finding out that Ayumi is actually a boy.

Shirokawa Sasane (30) is a former trading company employee and a huge fan of Romance of the Three Kingdoms. One day, after losing consciousness in Chinatown, he wakes up to find himself in the form of a little girl. However, the new body he finds himself in isn't just any little girl, but the granddaughter of the infamous tyrannical Dong Zhuo, Dong Bai. In order to avoid the fate of being executed alongside Dong Zhuo, Dong Bai will have to use both experience as a Japanese businessman as well as knowledge of the era!

Born as the illegitimate second son of Loxollum’s king, Iblonde is sacrificed by his pagan mother to ensure that one day, he sits on the noblest seat in the kingdom. A few years later, Iblonde has started a new life as Abel, a serf of a baron’s domain. Aside from his tragic past, Abel harbors many secrets, including the fact that he is actually a girl. But the greatest secret of all is that Abel’s resurrected body is now occupied by Belial, the seventh king of hell, who has come to slowly plague the land...

At first glance, the Fukuoka city seems like a peaceful one, but under the surface, crime is running rampant. The city's Hakata ward is home to the professionals of the underworld: professional killers, detectives, informants, professional revenge seekers, those skilled in torture, and more. And according to urban legend, even a “killer of professional killers” exists in the city. When stories of the men in the underworld are told, a “professional killer murder” appears.

At Fumidzuki Academy, classes are separated by academic achievement. The smartest kids are in A Class, while the dumbest are in F Class. This chronicles the daily life of the students in F Class. Instead of grades, they have to worry about homosexual stalkers, crushes, ambiguous genders, and waging academic war on the upper classes!

He became a magical girl, and his buddy fell in love with his magical girl form

Artist’s Twitter: https://twitter.com/isiyumi
Artist’s Pixiv: https://www.pixiv.net/en/users/1573847

This is the legendary Go Nagai's breakthrough work. Harenchi Gakuen is an elementary school whose teachers and students are all perverts. Boys peep girls changing. Girls pull up their skirts and show off their panties. Actually, it's not as evil as you imagine. They're like cubs playing together. It's only pre-school eroticism, nothing sexual. In spite of that, Harenchi Gakuen became a sensation. Parents, teachers, and politicians hysterically attacked the comic's immorality.

Hajime Nakano is forced by his mother to enroll at a newly opened all boys high school, and he laments over having to spend the next three years surrounded by other guys. However, he doesn't know that all of the other students are girls secretly pretending to be guys, and each of them think they are the only girl in the whole school.

Nishimoto Haruki is a 21 year old male and a newly recruited police officer. However, all his past assignments involved him dressing up as a girl in order to solve the crime. It seems that he has the feminine features that make him the only one suitable for the position. However, things get even crazier when he is assigned to be in the all female police squad surrounded by gorgeous women. He has to protect his secret that he’s actually a man but Haruki is already having a hard time controlling his urges.

The kingdom's hero, Ortus (♂), dies in battle after failing to fulfil a promise he made to protect the kingdom for the rest of his life. When he wakes up, he finds that he has been reincarnated as Seretina, the duke's daughter!

Even though she's a lovely, beautiful girl, she's still the same and determined to become a knight to protect her country in this life. However, besides being sickly and fragile, she is also faced with the harsh fate of a lady. She has to learn manners from her horrible mother, marry a man she doesn't want to marry, and many other challenges that will keep her from becoming a knight.

Then, on the way to the royal castle, a demon attack reveals her true power that no one knows about! A new heroine is born, with the strength to slay demons with a single blow, and the peerless beauty to captivate even people in high society!
She’s pretty on the outside, but fearless on the inside!
The chivalric, heroic fantasy of a feeble young woman begins!

An old man was laid off from his job at a black company. While wallowing in the depths of his despair, he encounters a mysterious stone that sends him to another world filled with magic and alchemy. The man finds himself reincarnated as Hiyo — the youngest daughter of the demon lord.

Hiyo attempts to make a dazzling fresh start in life by utilizing both her newfound magical powers and prior tribulations as a salaryman, however, the demon world is in the midst of a battle for succession. In order to change herself, the ex-old man is determined to defy the demon lord and her siblings. And after meeting Ernest, a hero with his own circumstances, they work together to take over the throne of the demon lord — for both the sake of peace and to search for a place to belong. The two of them defy destiny, even if it means destroying the world to do so...

From Easy Going Scans:

Chang An in the Tang Dynasty of China (618-907): The demon star is passing through the sky, calamity is about to befall the Tang Dynasty - because of a woman.
Skilled in martial arts and war tactics, Princess Li Chang Ge sets out to avenge her family and take back the throne.

“I hate men!”

Mao was harshly dumped by her boyfriend. She fell asleep while feeling totally dejected... and turned into a man the next day! Not knowing how to turn back, it was decided that Mao has to live in a dorm as a guy. However, her roommate, Ryuusei, is extremely curt and annoying.

How will her life turn out?!