Yataro Sarumaru, nicknamed Saru, is an ace in the locksmith trade and is obsessed with girls. This (almost) average teenager is given a hardly ordinary mission which marks the beginning of his adventures!

Mayuzumi Kasumi is the school Idol. However, she doesn't realize this. She just wants friends, but that's difficult when she unconsciously seduces all the girls.

From Fantasyshrine:

Watch the sparks fly between the two student body presidents of the so-called “Yuryo” brother schools, “Yusei School” and “Ryosei Academy”, as they fight for their rights for “Juliet”—!!?

I was a corporate worker in my 30’s, when I woke up and found that I had time leaped to the spring of my second year of high school. At the time, there was a teacher that I had regretted not confessing to, so I confessed to her in the heat of the moment, and now we’re dating! However, the teacher is one who would make any man a good for nothing person, so I end up being spoiled by her a lot.
While secretly dating my overworked teacher (lover), a sweet school life filled with flirting awaits. A 2nd year high schooler with a 30 year old me on the inside and the teacher (lover) that I want to pamper, our everyday romantic comedy begins.

From JShoujo Scans

I Can Hear the Ghostly Drum-Beating
The first guy Rika ever falls for turns out to be her older sister's fiancé. However, her sister's dream since she was a child was to be a bride, and ever since her engagement to another guy didn't work out a few years earlier due to her not being able to conceive, Rika swore to do everything in her power to help her sister fulfill her dream. Does that include helping her marry the guy that she's in love with?!

Like Snow Falling on Harbor
Yori runs into Kurita, a girl he knew from basketball club back in high school. Back then, she was a quiet girl who had a quirky oddness to her. When he runs into her out of coincidence two years later, however, he finds that she's become an out-going (if not slightly high-strung) girl. A few weeks after their chance meeting, he receives a phone call from the hospital saying she had tried to kill herself, and he finds out the true reason for the drastic change.

Fight!
Yuki's a hard-working 21 year old who's tirelessly slugging away as a coordinator at a English language school so that she can save enough money to go study abroad. She has no interest in guys because she's so set on her goal---that is, until she meets Yuki, a guy with the same name as her. They move in together only days after they met, and at first things go well, but one day, he hits her in the face by accident. The violence escalates as the days wear on --- will their love last?!

The Days of the Sun
Nana and Ichi are twins who are as close as can be. Sure the people around them think it's odd that they still sleep in the same bed --- but they couldn't care less what others think. All they need is each other. One day, they run into a scruffy looking man wearing dark sunglasses who claims that he's their long-lost dad! Is it really him? And why did he choose to reveal himself to them now?

Includes other stories which all center around the theme: "a rose-colored tomorrow."

Takayama, a teacher living his teacher's life "going on with the flow", is being scolded for his lazy attitude by Fuyuno, the most talented female student in his grade. In fact, Fuyuno has special feelings for Takayama...? Can the forbidden love between a teacher and a female student be avoided?

Manaka Sakiko is a huge fan of Chihiro, an idol from the idol group Haruiro Sunshine, and on her first day of high school she finds out the new girl sitting next to her is none other than Chihiro herself. No one else recognises Chihiro, so Sakiko resolves to keep her knowledge under wraps, but when she accidentally slips and reveals she's a fan, she unwittingly makes herself the enemy of another Chihiro devotee, one who isn't keen on sharing.

Present day, present time. For some reason, rare newborns get swapped with the newborns from another world. They have the features of legendary creatures (like dwarves, oni, harpies etc), however, they lack the abilities of their legendary predecessors. Our heroine, an elf girl Kazamori suffered through her childhood because other kids expected her to wield magic like a true elf. She tries to uphold her "magic user" image in high school but the person who finds out her secret is an ordinary human who practices magic-like science.

A mecha otaku is reincarnated into another world as Ernesti Echevalier (Eru). In this world, exist huge humanoid weapon known as Silhouette Knight. Dreaming of piloting those robots, Eru, with childhood friends, Archid and Adeltrud Olter: together they will aim to become Knight Runner, pilot of Silhoutte Knight.

Hasegawa Kodaka has transferred schools, and he's having a hard time making friends. It doesn't help that his blond hair tends to make people think he's a delinquent. One day, he runs into his bad-tempered solitary classmate Yozora while she's talking animatedly to her imaginary friend Tomo. Realizing that neither of them have any actual friends, they decide that the best way to alter this situation is to form a club and start recruiting.

That is how "Rinjinbu" was formed, a club specifically designed for people who don't have very many friends. As other lonely classmates slowly join their little club, they'll try to learn how to build friendships through cooking together, playing games, and other group activities. But will this group of relationship-challenged misfits really be able to get along?

Age 41, Oh Joong Seok. A man who did all kinds of misdeeds and put his life on the line for the organisation to gain the highest position. But who knew the end of his life would be so miserable… Joong Seok’s ‘virtuous living’ project starts now, one by one.

Miko leaves the house of her parents to live with her uncle who runs a boarding house, but her first meeting with Matsunaga-san isn't good and then he discovers that she is one of her uncle's tenants. Even as a secondary student she surrounds herself with university students who have a very different life from her own. Can she fit into her new home?

Lizardmen are hit by disasters today in a high school, where there are various races such as elves and beasts. But this lizard is quite delicious, and I'm sick of it!

Receptioning the newcomers is a task for YuYang, and he ends up helping the unsociable and towering LiHuan, the kind of person that does everything to be disliked. But after better knowing each other, he discovers that the giant isn't that bad of a person at all ...

A high school student, Akito who hates people around him, accidentally took a picture of a passing by young girl during his daily routine of taking scenery pictures. Then, He realized it was the girl who recently transferred to his school. He planned to talked about the accident of him taking the image but... somehow the girl he took looks different?

Large mysterious alien ships have been looming above Japanese towns for three years, filling the sky. Everything changed three years ago. And yet, nothing has changed.
No weapon used against the invaders' ships had any success, beyond destroying part of Japan and leaving its economy in shambles. JSDF is fighting a guerrilla battle against the aliens all over Japan. America is joining the 'war' effort with more aggressive tactics, dividing Japan over the pacifist principle laid out in Article 9 of the Japanese constitution. But this may just be the mundane story of young high schoolers.
"No matter what happens, I won't back down.
At least not until this world filled with lies and deceit crumbles away. The real threat to humankind is not invaders, but me."

The stage is a modern school that fosters female officers, "Girl's Only Army School".
A girl, Indou Shinobu, who came out from the countryside, meets Kagami a high-class senior student.
Contrary to her high-handed attitude, Kagami occasionally shows kindness to Indou.

Aoki has unrequited feelings for the girl sitting next to him, Hashishita-san. That smile was like an angel’s, charming, clenching his heart every day. However, ended up seeing a male classmate, Ida’s name written on Hashishita-san’s eraser...?!

Sakurai-san is reminiscent. I'm entangled with me and I'm watching this when I notice it. And I always turn my happy face at that time. But if you're serious and like me ... A battle of love while being disturbed by girls' gestures!

In this world, when human beings reach the age of 12, their bodies gradually change to the genders they wish to be. And by the time they are 14 years old, their appearances change to reflect their genders. But by spring of my eighteenth year, I am still without a gender...