In the Viking Brides series:

1-Byakuya no Princess (The Reluctant Princess)
Elli has no memories of her homeland or father, having been raised abroad by her mother with her sisters. When a mysterious man breaks into her house, she finds out that she’s royalty of the far-off land of Gullandria, and that her father is the king! With a reunion in the cards, will Gullandria prove to be all Elli hopes, or will she escape into the arms of the man who brought her there?

2-Gekka no Ayamachi (Prince and Future...Dad?)
Princess Liv Thorson honestly believed she could skulk back to America, her uncharacteristic night of passion a secret known only to a sympathetic sister...and the Viking prince who possessed her underlisse. Then came the baby trifecta--woozy tummy, fainting spell, rash--telltale signs that she and Finn Danelaw had made a lot more than love....
Finn Danelaw was used to hearing all kinds of utterances from women, but "no" wasn't usually among them. He had, however, a proposal for beautiful Princess Liv...and though he'd planned a seduction along with it, he'd learned a long time ago that all good things come to those who wait. For the test results, that is. The pregnancy test...

3-Shukumei no Deai (The Marriage Medallion)
He’s going to be my husband? Princess Brit is forced to marry to preserve the royal bloodline, so she flees the palace and heads for the distant North Sea. But on the way there, her plane crashes, and she is thrown against the steep cliffs. She’s hurt and terrified! As if in answer to her pleas for help, a dark shadow appears. Is he the legendary black knight? No—it’s Eric Greyfell. He’s as beautiful as a hero from Norse myth, but his heart is as impenetrable as a stone statue. And he’s the man she was expected to marry!

4-Kamen no Prince (The Man Behind the Mask)
Dulcie has arrived at a foreign palace to celebrate the wedding of her best friend, the princess of a small country. There, she meets Prince Valbrand, a man with a scar on his face. A hideous burn scar, marring the face of a beautiful man. What cruel fate must he have endured? On the night of the ball, spurred by curiosity, Dulcie dances with him and realizes that she has fallen in love.But as Dulcie grapples with her emotions, a tragedy awaits.

Allen, an eight-year-old boy from a poor family in the royal capital, is living a poor but happy life together with his mother. One day, however, memories of his previous life suddenly come back to him and he remembers that he is in an dating sim game and that the capital will be destroyed by war if he doesn’t do something about it.

If this continues, both he and his mother will be killed!

With a sense of urgency, he decides to rise to the occasion in order to save his precious mother’s life and save his favorite character, the villainous young lady Anastasia, the only girl he liked in the game, from her all too tragic and ruinous end.

This is the story of a man who isn’t even a character in the game, but who strives with his steely determination and uses all the knowledge he has to turn overcome fate!

Original Jp Web Novel: https://ncode.syosetu.com/n6755gk/

Heo Jeong-woo, a high school student who is bullied by a girl in his class for his weakness.

Han Bo-ra, a transfer student, comes to Jeong-woo's class, where he was spending his miserable days.

Jeong-woo feels a strong sense of déjà vu when he sees the child with straight black hair and stains on his legs. Sure enough, Han Bo-ra, who has subdued the arguing classmates, asks them.

"'Have you ever seen a child similar to me?

Jeong-woo decides to approach Bo-ra, who might be able to correct what is wrong...

Ling Chen lived as a villain for 35 years, but in the final battle with the hero Ye Muxue, he "initialized" reset-reborn back to 17! what? Do you think he wants to be human again? Less talk! Of course, it's time to kill Ye Mu, who wasn't super powered at that time!

"You must become the greater evil to fight against the real evil!"

Cassian dies after being framed for the murder of a comrade. Just when he thought it was all over for him, his soul is transferred into a young boy...

A popular, top-class Psyker who was everyone's envy turns into a Villain overnight!

When I woke up, I discovered I had become the villain in the martial arts novel I wrote! But of all people, why does the body I possess belong to a damn villain?

Hyuk Ryun Woon:
The fourth son of the Demonic Cult’s Leader
A nasty womanizer
A martial arts weakling with a filthy temper
A worthless villain who is one shotted by the main character in the novel!

If I don’t want to be killed by the main character, I have no choice but to become strong.
“Fucking hell. The main character and whatnot, I’ll wipe them all out!”
The Shaking Tale of a distasteful villain who uses whatever means necessary to survive!

I reincarnated into the "Villainess Eumiella" from an RPG Otome game. In the main story, Eumielle'as merely a side character, but after the ending, she reenters the story as the Hidden Boss, a character on par to the Heroes with her high stats!!

Lighting a fire in my gamer's soul, and taking advantage of being left on my own in my parent's territory, I train! Train! And at the end of my training...... By the time I enter the academy, I managed to reach level 99.

Though I had planned to live out my days as inconspicuously and peacefully as possible, soon after entering the school, I'm suspected by the Heroine and Love Interests of being the "Demon Lord"...?

A popular Web novel of seeking a peaceful life, a fantasy story of the strongest villainess!

As a child, Thorfinn sat at the feet of the great Leif Ericson and thrilled to wild tales of a land far to the west. But his youthful fantasies were shattered by a mercenary raid. Raised by the Vikings who murdered his family, Thorfinn became a terrifying warrior, forever seeking to kill the band's leader, Askeladd, and avenge his father. Sustaining Thorfinn through his ordeal are his pride in his family and his dreams of a fertile westward land, a land without war or slavery... the land Leif called Vinland.

Note: Was nominated for the 2008 Manga Taisho award. Won the Grand Prize in the manga division of the Japan Media Arts awards in 2009. Won the 36th Kodansha Manga Award for Best General Manga in 2012.

Animal parody of the manga Vinland Saga

From Batoto:
Kikuno Kei, nicknamed "Kay", is a normal university student and a part-time hitwoman.

Masamichi Akita, a high school student whose motto is to live wisely, who meets Setsuna Rikudou, a high school girl with a violent supremacist attitude.

Akita is saved by Rikudou when he is tangled up with a delinquent, and is attracted by her overwhelming strength, asks her to teach him how to fight. However, Akita is devastated by Rikudou, who asserts that “violence is the only rule in this world”.

Akita's encounter with Rikudou leads him into the world of “violence”.

September 11, 197x, In the whole Kantou region a magnitude 8-9 violent earthquake occurred. Scholars called it the great destruction of the Showa Era, but the people called it the earthquake from hell! Volcanoes erupted, buildings crumbled, Tokyo became decimated in a single day. The government, after failing to recover the city, abandons Tokyo and moves the capital. The survivors form a society with no laws. In this harsh lawless world emerges Jack, a 10 foot giant who annihilates anyone and anything in his path. The manga details his journey.

A Violence Jack one-shot from 2001. What happens when Jack and some bikers mysteriously get sent back into the age of samurai.

A stupid and tall student, Myouenji, loves a small but delinquent student, Kuroda. Myouenji keeps stalking Kuroda though he knows Kuroda adores Masaki, a very cool guy. But soon after, Kuroda kisses Myouenji by mistake instead of Masaki...

Sold for 20 gold as a lifetime apprentice to Wudang Wudang in the serene cloud, how will he deal with the impoverished Wudang College's daily life? What kind of hilarious hijinks will Emei, Kongtong, Huashan, and the rest of the gang ensue in the school? Who will be selected for the highest institution of martial arts?

Violet is a girl whose mom pays no attention to her, or her father. What Violet wants more than anything else is a pretty dress and cookies that the other moms make. Then, one day, she meets a lady at the park who gives her what she desires...

A story of a young girl, Yin, and her passion for the violin.

Warning: This is not a romance!

Pandora's Box led a cursed existence. Through the curiosity of a woman, evil was unleashed and very nearly covered the world in darkness. Miraculously, humanity managed to seal Maou Kestra back into the box, but only with immense sacrifices. Even without their lord, the demons are still a formidable force that has only grown stronger with time, locked in the abandoned capital of the North, Hameln. Fifteen years have passed since that fateful battle...

Enter Hamel, a travelling minstrel who is so self-centered that he'd sooner cook his guardian crow (and family friend), Oboe, than go hungry for even a minute. Welcome to the world of music and hilarious insanity that is the Violinist of Hameln. Watch as Hamel takes cheap shots at his opponents and bashes pigeons with his giant violin and turns them into dinner.

How WILL the world be saved from Maou Kestra (it's a pun for orchestra, if you haven't noticed) with a hero such as this?

This is the sequel to Violinist of Hameln. So read that first.

This series takes place in a fantasy world with famous composers' music, magic, friendship and dark secrets. Our main character of this story is a young ambitious, energetic boy named Schel. (Scale, as in the musical term) Because of the general of the MagiCorps saved Schel from a Mozoku (Monsters of this world) he has a dream to become the greatest magician ever. So he travels to the capital Sforzando the magic city and enters the MagiCorps School of Magic. There he meets Great, a violin magical music user, who is also the son of the great hero Hamel, who defeated the Demon King Chestra. As Schel tries to become the greatest magician, he also holds some secrets of his own. But how will Schel survive magic school with so many rivals to compete against?

From Chibi Manga:

My papa isn't my real papa. His real form is a vampire. He raised me up since my parents passed away. For the moment when he could eat me...