One day, a mermaid saved me from drowning...

From Viz:

Riko Kunimi is trying to lead a normal high-school life when Ran Tachibana bursts into her classroom carrying a gun and tells her that her life is now his. Ran, the richest, most powerful 17-year-old in Japan, wants her as his wife, and he's not taking no for an answer!

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Also included in this manga are the following stories:

- Jigoku Kokyuu no Hitsuyou (Vol.1)
Kiyoharu was trying to nap when a girl kissed him because she thought he was dead. He later learns that Touko, the girl, is always kissing someone in response to not being able to breathe and feeling suffocated.

- Fureru Ondo (Vol.2)
Kashuu hates being touched because of his past experiences. He will only let Sayuri-sensei, the biology teacher, treat his wounds. To him, Sayuri-sensei's touch is precise and practical without bring up bad memories.

With her love lost, Miwako promises to give her beautiful hands to the handsome demon Rin.

Akimoto Yae is a cheerful - and sometimes exceedengly loud - girl who secretly always watches her sempai Ayase, who rides the same train as her. For some reason, Ayase always sits in the same seat, holding the same book, opened at the same page. His hands never try to turn to the next page.
One day, Ayase accidentally drops the book, which comes as a chance for Akimoto to talk to him. Much to her surprise, he isn't interested in having the book returned, and gives it to her.
As Akimoto tries to overcome her mild aversion for printed texts - which causes her to sleep if she doesn't read the lines aloud - and read the book, she hopes to get closer to Ayase, which has reasons of his own to be aloof.

Nakamura Mei is a very simple high school girl. While at a cafe with her friends, they bump in to -none other than- the model Shirou's table. Mei apologizes and that's when Shirou notices something. Grabbing her he takes her outside with him and reveals that Mei was once a kids model—and that he's her idol-otaku!?

(Source: CoyoMoose)

Note: The short stories in volume 2 are Anya Kouro and Wonderful Cafe ni Youkoso.

From Aerandria Scans:

Nanao came from a rich family before their business failed. Now the only hope for her family to pay off their debts is if she can cement a marriage with the prestigious Takatsuki family within a week. How will Nanao overcome this problem when one of the three eligible Takatsuki men is her former arrogant schoolmate, Yoshito, who completely distrusts people? And did we forget to mention that Nanao is already the ninety-ninth candidate for the position of future wife?!

Taiga Shishio, the Student Council President, is a notorious tyrant. And yet, the only person that can stop him is his faithful Vice President Momoko. School, love, and trouble collide in this amazing story of student leadership!

Ichihara Yui is a 15 years old high school girl. On the first day, she meets Itsuka Daisuke and mistakes him for a teacher. To her surprise, they meet again in the classroom but he is in fact a high schooler too. Indeed, Itsuka is 25 years old and he wants to enjoy the high school life he has never been able to get ten years ago.

Ten years ago, Nachi and Iori were adopted by a government official. Now they work under him as bodyguards in the Secret Protection Agency "Shelter." However, despite all this shared history, the two can't seem to get along. Will this next mission be their breaking point or bring them closer together?