I am cute, but I was a middle-aged researcher in my previous life?!
Surviving in another world with magic and sciences!!
The orphan Ren was riding the carriage after being sold, when she got involved into an accident, and got her previous life's memories back!
"I was... a middle-aged man!"
Indeed, she was a researcher in his thirties in her previous life, and had been living as an orphan girl up to now!
Ren will make use of her talents in magic and knowledge in science to survive in this harsh world in order to escape from the investor who bought her!

It's about a Chinese God in the modern century.

From a young age, Minami Harusumi has had recurring dreams of Veronica, a princess whose kingdom is on the verge of destruction. He believes them to be recollections of his past life, and that he is her reincarnation. Because of this, he is ridiculed by his classmates. One day, when the mockery escalates into bullying, he rediscovers magic - something Veronica had studied and used. Reassured his past life is not merely a fantasy, Minami tries to learn more about his past memories and the reason behind them...

An ex-pro gamer of the FPS genre (♂) reincarnated in a fantasy world filled with magic... Only to learn that what greeted him was not a scene from one's dreams, but a muddy battlefield full of bullets flying to and fro! Moreover, he's now an orphan girl named Touri Noel?!

After her aptitude for healing magic was discovered, she decided to volunteer in the army as a second-class medic, all to raise money for the orphanage where she was born and raised. However, without even getting magic training, she was attached to an assault squad, repeatedly fighting on the most cruel battlefields of the "Western Front."
The mission given to her was to become the personal medic of the frontline's ace, Garback, and not let him die at any cost. But he turned out to be the worst commander, who will try to get results whatever the cost, even if it means the death of his subordinates!

On the battlefield, mired in unreasonable orders and violence, Touri's fierce battle for survival continues...

As the master of the School of Unholy Arts and as the undefeated Unmasked Demon, MookHyang unfortunately falls to a strange fantasy world by the magic of his enemies (School of Blood Arts). In the new world of elf, sorcerer, knight, and dragon, MookHyang’s adventure of finding a way back to his old world (Murim) unfolds.

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!?

A polite and lethargic boy was reincarnated in another world as a vampire bishoujo. In this world of swords and magic, this protagonist who was reborn replete with all kinds of cheat powers was searching for one thing――! “Three meals a day, snacks and an afternoon nap, I guess.” Are you really the protagonist! And thus begins the fantasy comedy of a vampire looking for the ideal moocher lifestyle…?

Albright, who was famous as “the strongest Black Knight”, was reincarnated as a girl, Maria, whose ribbon suited her well for same reason. Maria, 16 years old, is currently a maid in the Marquess of Urband family in attendance to the Daughter of the Marquees, Relena. After Relena became engaged to the 4th Prince, the area around Maria had gotten busier…

Shunpei, a loner high schooler, became a gyaru after saving the god of gyaru from drowning. Through his mother's connections, he was able to transfer to an all-girls school, but it was stuffed to the brim with gyarus!
Every day is a sensory overload for Shunpei, who's never even talked to a girl, let alone a gyaru.

It's the beginning of an introverted high school guy => gender-swapped gyaru comedy!

Uesugi-kun is a boy who's as petite and cute as a girl. He has a crush on a girl he's known since childhood, but overheard her saying, "Wouldn't Uesugi be totally adorable if he was a girl?!" Uesugi-kun's not as tall as his other childhood friend, Eito, nor is he as good at studies, and now he's suffering from a broken heart. A depressed Uesugi-kun stops by a shrine while running an errand and makes a wish... A love-triangle romantic comedy featuring an overly cute, and now female, protagonist begins!

A humble man in his twenties suddenly dies and is reborn as the daughter of a duke in an 18th-century lookalike world where magic exists!
He is now living a second life as the adorable "Miranda Mirandiehl," who looks like a doll.
As he was always a "girl inside" with girlish interests, he accepted his reincarnation surprisingly easily.
And so, after being reborn as Miranda, he will enjoy his new life to the fullest!
What kind of encounters await him, and what lies ahead in his gender-swapped otherworldly reincarnation life?

Both of them are straightforward people. Once they meet, they quickly get to know each other better. A heartwarming romantic comedy that begins with a certain incident. Shibata Kasane, a graphics designer at a toy design and development company, is troubled. Her troubles started when she grabbed her colleague Enokida Subaru's ass by accident! Kasane was intrigued by how similar Enokida's ass and her favourite childhood character felt. At the same time, Kasane felt guilty because Enokida might have been uncomfortable. Enokida said "I don't mind" but had a pained and frightened expression. Kasane was overcome by the urge to apologise profusely! On the other hand, it looks like Enokida is hiding something.

The story of a crossdresser who receives a confession from a junior.

Kang Ji-hoon, an ordinary high school student who died in a painful accident, finds out in the underworld that he is actually a ‘Water Spirit King mistakenly born as a human’. “Making water spirits? How do you do that?” The adventures of Elqueeness, the Water Spirit King who was mistakenly born as a human!

A hitman and a marriage swindler set out on the world’s most grueling battle for marriage! Gero is a young man from a clan of hitmen, which has been in existence for hundreds of years. As someone who’s never gone to school and lived his life dealing in the dark side of the business, he considers himself to have “no prospects with women” and marriage as “something not for him.” However, one day, in fear that their lineage would dissolve, his clan warns Gero that if he doesn’t marry and produce an heir, they would have no choice but to…force his little sister into doing “that.” Driven to his wits’ end, Gero asks the target of his work, a marriage swindler, to…

A dull old man and his handsome best friend were summoned to another world by a naked goddess! However, because of the goddess's mischief, he has turned into a peerless beautiful girl?! To get back his body, he has to go on a journey with his best friend to defeat the demon king!! "An old man that became a beautiful girl" and "A handsome old man"! Let the madness filled another world journey rom-com begin!!

Misaki-kun may be adorable, but he's just the 'best friend' type character you can find in any gal game. However, the protagonist, Kihara Hareta, isn't set on wooing any of the heroines; he has his eyes set on the Unobtainable Misaki-kun! Gender makes little difference in the face of such cuteness in this heart-stoppingly sweet comedy!

From MangaHelpers:
Nogawa Izumi is a good student, and a class representative, but she has an increasingly high libido. It's gotten to the point that she'll claim to feel bad during class, so she can run to the nurse's office and masturbate. When she learns that the Earth is being invaded by aliens that look like people dressed up as animals, it turns out her high sex drive may be able to help protect the Earth. The first time Izumi is attacked by the aliens, she is rescued by Usayama, a bunny alien whose race was their previous victim. Usayama gives her a swimsuit that will allow her to fight the aliens, but which also sends her constant arousal through the roof. The scientific organization that Usayama is affiliated with think that Izumi, with her high erotic level, may be the person they've been looking for to fight the aliens. Will Izumi be able to save the Earth?

Although she had been a promising practitioner of kendo in the past, due to an accident she was forced to lead a plain life. After Seo Yuri gets into a car accident during a trip back home, she reincarnates into the novel, "The Song of the Moon," and becomes the elder twin sister of a side character who meets a destructive ending-- Selena. Selena hopes to prevent the destruction of her family, however, she is forced to take the place of her runaway brother, Celestine, in the knights’ squadron! Will she be able to avoid the villainous Crown Prince, Ignis, and survive?!

Disappointed that the girl he loves does not return his affections, Eitaro attempts to commit suicide. But his near dead-body is discovered by a scientist and his mind is transferred to the body of a young girl. As a girl, Eitaro soon learns that the girl of his dreams did in fact love him, so they try to make the relationship work despite the fact that Eitaro is in a girl's body.