From 200 wpm:

Once upon a time, there was a mermaid: "I want to become human so I can fall in love" she said. When her wish was granted, the lower half of her body turned to foam and she became a human... MALE ♂!?

This is the love story of a 30-year-old virgin man and a beautiful (male?) mermaid!

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From LuffyNoTomo:

A 30 year old man named Koganei, Manato is down on his luck. He can't seem to get a job, has little money, is still a virgin and is giving up on his dream. Sitting alone on a swan boat in a pond next to a shrine, he holds a lottery ticket thinking this is the only way his dream may come true. But the wind blows it away and he falls into the pond, thereupon seeing a beautiful mermaid!

Manato ends up going back to the pond and after the mermaid decided not to kill him since he gave her food, she tells him about her dream to become human and how she wants to find love (she collects coins and throws them to a shrine in order for her wish to come true). Manato decides he doesn't want to get involved anymore because he has his own worries, but after another bad day he goes back to the pond. She finds him again and after listening to his complaints, she decides to give him all her saved up coins in order for his wish to come true. She suddenly turns into bubbles and disappears.

Confused and upset, Manato hears a strange voice and a god from the shrine comes to say that she will take the coins and grant him a wish. He decides to use his wish to bring back the mermaid as a human. His wish comes true and he sees the mermaid back as a human, but she's a guy! What will happen in this crazy love comedy!?

From Baka-Updates: In Asahi's school, there's two tipes of students: the ones from the elite class and the average one. After an accident in her house, she starts living in the rooms of the elite class but no one must know, or else she would be expelled. A black hair guy from the elite discovers her secret, what's going to happen to her?

From Esthétique:

Sakura had lived with her grandma ever since her parents died in a car accident when she was three. When she turned fourteen, her grandma also passed away, leaving her alone. Just when she was about to give up hope having a family, out of nowhere, four guys claim to be her older half-brothers.

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- Himitsu no Tobira no Kugurikata (Vol. 4)
Terasima Tika has always wished to meet her prince charming. When she accidentally enters the 'Spirit Door' and is placed in the body of her brother, she is forced to be him for the day and go to an all boy's school where she hopes to finally meet her prince.

A two-part oneshot about the story of a lonely god and a troubled high school girl.

The remarried mother. After their divorce, the father who lives with his "boyfriend".
Living surrounded by such family, highschooler Mayuko is now at the height of her adolescence. Beginning from Mayuko's "runaway", intersecting various life, these are the runway story which will dye in to your heart.

The lead is a spirit medium, although unfortunately he's not the best. His medium house has lasted for generations, but he only has a quarter of their ability - the only spirits he can call are animals, and while his touch can feel the spirits, he can't even hear them. For that, he needs help from his feline sidekick, although he can only be called half a cat, as he has the past life memories of a dog. Together they aid the animals they encounter, helping them find perspective by exploring their pasts.

A group of 5 male high school students that call themselves the funny-face group cause trouble at school with their crazy antics.

The thought of going on a field trip and taking a bath togther with Ricchan makes Fuuchan a mess.

Two parts oneshot from Comic Lily vol. 1 and 2

Newly-transferred girl, Oribe, falls in love with the most popular and charismatic boy of the school, Sagara. But, Oribe is not what she seems? The tale of the mecha girl with the heart of a maiden unfolds!

Hosaka Mao's never stood out. Her father's a washed-up rock-and-roller. Her hair reminds people of Pippi Longstocking. She's nowhere near the in-crowd. The arrival of long-haired beauty Hasekura Yokiko changes everything...

From Which Scanlations:

One day, Kengo Yagami found some of his classmates teasing a turtle that lived behind their school--and he beat them up. But when the turtle spoke, he was so shocked that he kicked it as hard as he could. Unfortunately, the turtle was actually a god, and as punishment, he switched Kengo's body with his childhood friend Mitsuka's, and their new bodies are causing both of them a lot of trouble at school...

Also includes the one-shots "Kirakira Hoshi no Ana" and "Kimi wa boku no Saboten."

A collection of oneshots.

Story 1, Rabbit Costume: In a closed-off town, there is a strange disease in which people disappear along with all memory of them.

From MangaHelpers:
High-schooler Matsuzaka Satou has a reputation for being easy, but one day her lifestyle of sleeping with one boy after another comes to an end. It happens when she meets the child Shio, for whom she is convinced she feels true love for the first time. Satou may seem sweet and innocent, but there is nothing she won't do to protect their life together, including committing murder. But from where did she acquire the little girl, and how long can their "Happy Sugar Life" together last?

Included one-shot:
Volume 2: White Sugar Garden, Black Salt Cage (pilot)

Short story:
A short story was released in Young Gangan 23/24 of 2016 which is referred to below as 19.5. It was later released in Volume 6 as an extra.

Chiaki inherited the house of his late great uncle, who was a shaman and starts living there. When he finds a mysterious ring and puts it on, he accidentally summons a beautiful demon fox.

Reki is a high school girl that always acts cold and isolates herself from others. Yuta sitting next to Reki keeps trying to be friend with her in every way possible. However, her cheerful approach to Reki only makes her extremely puzzled and overwhelmed. At this time, the class president Maria gets in the middle of these two. Would she make things work for them or cause more troubles?

A short twitter series by @udon0531.

A story about a guy who doesn't think that he is in love.

This boy looks so cool, so it can't be helped if I fall in love. “We've been so close ever since middle school, so now, I can't tell him I like him...” is what Akemiya feels with an unrequited love towards Iwata. But upon entering high school and becoming friends with the two popular hotties, Fujiwara and Shirotaki, Iwata is starting to get cocky!!
Iwata and Akemiya, the super popular side characters of “Fujiwara-kun wa Daitai Tadashii” presents the long-awaited super popular spin-off series that will make your chest squeeze, give you warm fuzzies, make you laugh and make you cry ♪.

Masato, adoptive son of the Kuwabara household, has always been surrounded by prosperity... Until one day the head of the family brings home a child named Kenta. Drowning as he is in the despair of having outlived his purpose, Masato still doesn't fail to notice the undue attention the master has started paying Kenta...

Short comedy spin-off for Koi Dano Ai Dano, follow the quirky adventures of Kanoko and her high-school classmates and teachers!