From Aerandria Scans:

Who am I? I'm Gi-ryum, a tall, handsome bachelor, and the coolest guy in the country who even makes O△ sama (Reference to "Yon-sama": Bae, Yon-Jun from Winter Sonata) cry at my beauty. One day, I received classified info of the princess enrolling in a regular high school. Huhuhu. Can I snag the princess with my irresistible beauty?! I will be the king's new son-in-law!

"What is the boundary between game and reality?"

The world is in danger. Strange juggernauts called "Angels" have started to appear all around the planet, presenting riddles called "Paradoxes" to whoever happens to be in the near vicinity. Answer right and your land will receive God's blessing. However, if you fail to solve the paradox be prepared to receive divine punishment...

In order to live by his principles of never losing a fight, high schooler Kanzaki Ryousuke will run from everything to win! …or at least that’s what he wants to do. Even though he always tries stay away from trouble, he saves his classmate Ikasa Kaede from a fight. Will Kaede be able to steal Ryousuke’s heart with his piercing gaze…? Suddenly, the transfer student Amano Fumi who made a promise to marry Kaede appears?! A heart pounding school love story about their unripe love! A second volume about Fumi and the playboy Zono’s perverted times together and rough sketches included!

Hard-working Kusano Nanoha is about to graduate from high school. Through the seasons of being the basketball team’s manager, she’s grown close to her underclassman, Tachibana Kousuke. Will they be able to convey their feelings before Nanoha has to leave?

As kids, Rei always protected her best friend, Ichino. After being separated for eight years though, their roles have reversed: Rei is now bullied by the girls in class and Ichino is more outgoing. But Ichino says she’s become stronger for Rei’s sake, so she’ll protect Rei no matter what...

Two guys: cousins, both left-handed, both passionate about becoming their school team's best pitcher. One of them has already lost the spot once - back in elementary school - and his cousin moved away not long after, seemingly clueless to the fact that he was leaving the guy who introduced him to baseball dispirited and defeated.

Now, Yoshizawa Sora is back, still smiling innocently while encouraging Yoshizawa Shuuji to get back into the game. Shuuji accepts, determined to defeat the guy who, in his eyes, took away the only thing that mattered to him.

Hana, a country girl, has to move to Tokyo because of her father's work, and what's this? Her school is like a castle, her classmates have their own chauffeurs, and everyone is all sparkly and beautiful?
"I didn't realize that at the same time while my world was changing, my indecisive love was also starting to bud..."

When skipping class leads to unforeseen complications...

Sotomura is a high-school girl who is feared as a delinquent and avoided by most students. From her light-brown hair down to her long skirt and harsh manner of speaking, she completely seems the part.

But after Sotomura rescues a girl named Haruno from some bullies, Haruno decides to try to get to know her better. Haruno is surprised to find out that Sotomura isn't a delinquent at all and is, in fact, just a very socially awkward girl that's bad with words but wants to make friends. She enjoys cooking, handicrafts, and hitting the supermarket sales. Sotomura also loves cute and fancy things, but she hides these girly traits because she feels they don't suit how she looks.

Haruno's first step in helping Sotomura is to try to teach her how to smile, because whenever she tries, it ends up as a scary grin. Thus begins the story of Sotomura's attempts to make new friends.

Machida-kun seems like the perfect brother, son, and student because he loves people. Helpful when he needs to be, but puts himself down when he feels like a total failure. However, the people that surround his daily life are there as a reminder as why Machida-kun needs no improvements because the people love Machida.

Note: Nominated for the 9th Manga Taisho Award in 2016.
Won the New Creator Prize at Tezuka Osamu Cultural Prize awards in 2016.

From Viz media:

Timid and self-conscious high-school student Karin never paid much attention to boys until she met Kiriya, a popular student from a nearby boys' school. Karin and Kiriya embark on a romantic journey despite Karin's classmate Yuka's best efforts to sabotage their relationship, but Karin soon learns that living happily ever after isn't on the curriculum when she becomes Kiriya's center of attention, as well as embittered Yuka's bull's-eye on her dartboard of hate.

From Lezhin: Yeon Jang Hwa is a more or less average college student: she attends a pretty good university, is not too ugly, and has a nice boyfriend. Her a twin sister, Hong Reon, on the other hand, is the opposite. Being the good sister she is, Jang Hwa sets out to help her twin sister... but at what price? The truth is in the details. Original Webcomic http://www.lezhin.com/ko/comic/twin 

Kira believes that Rei and all other men in the world are dirty. She stays away from her classmates, hiding in her art. What happens when the delinquent motorcyclist and playboy, Rei, gets a hold of one of her drawings, and actually wants to keep it?

The first story, Namae no Nai Uma, is a ＭＡＲＳ prequel telling the first meeting between Rei and Tatsuya and the beginning of their friendship. Moreover, they've also presented other main characters such as Kira and Harumi.

The second and the third stories, Nemuru Raion and 1 Karatto no Kajitsu, are oneshots not related to ＭＡＲＳ.

The first tells of the strange relationship between Isomu, a guy who pretends to not have any fear, and Ayame, a girl with particular behaviours; on the contrary, the second tells of Nina, who has some family problems, and Rui, her classmate who is interested in a close friend of the hers. But what if he's interested in Nina?

The story takes place a year after the ending of Worst, when Sajima Yousuke and Miyamoto Sanmon are seniors at Suzuran High School.

As of May 2018, the last work in Takahashi Hiroshi's Crows x Worst universe by the original author himself. A two chapter gaiden story about a younger generation of Suzuran's crows, released in 2015.

From Aerandria Scans:
Mika is just a normal high school student who dreams of having a wonderful love. And then one day, she happens to meet Hiro, the guy of her destiny. While experiencing many sad events, and while getting hurt, the time she spends with him is still one of the most happy moments in her life...

Though he seems completely indifferent to romance, high-schooler Manabu works part-time as a writer for an erotic magazine. One day, right when some classmates were about to pick a fight with him, he was saved by Yamaguma, an underclassman. Apparently Yamaguma, who is popular but unfamiliar with romance, is upset about his older sister working at a nightclub. While trying to desensitize Yamaguma of his excessive reaction to Manabu's erotic writing, they...? The heat of their connected hands is the folly of youth. A bittersweet diary of first love.

After recently moving to Onomichi, Hiroshima, high school student Tasuku Kaname is thrown into despair at the possibility that he may have been outed for being gay. Convinced his life is over, his despair turns into shock when he sees a woman jump out of a window of a nearby house. Tasuku races to the house in a panic only to discover that it's a public meeting lounge owned by the woman he saw before. Tasuku comes face to face with the woman as she walks past him unharmed, but not before she implies that she had been watching him from afar. Confused, Tasuku follows her up to the top of a steep hill where she offers to briefly listen to what's on his mind. Although Tasuku doesn't go into too much detail, he later accepts her invitation to come to the lounge to meet others with similar troubles.

Protagonist Sakuragi Ryou was in the "A group" in middle school. At least until he got caught up some trouble and developed a reputation as a delinquent. Wanting to live a normal, peaceful life in high school he decides to do a reverse high school debut, aiming to be in the boring, middle-of-the-pack "B group". Above all else he doesn't want to stand out. But then one day he encounters the school idol, Fujimoto Erika, being harassed by delinquents and begrudgingly decides to help her out. She then starts to develop an interest in him, which is going to make his goal of not standing out tough...