Death March kara Hajimaru Isekai Kyusoukyoku (WN) - Chapter 545 - Sisters

There are 5 books on the 6 sworn brothers in a serial called streamer (流光系列). ‘They are rich, handsome and powerful. These book are on various types of love as well as on the bond and mateship between the brothers. Book on youngest 6th brother.

Chen Yu Bai (3rd brother) & An Xiao Yi – Chen Yu Bai is a sharp, domineering & cool man whereas An Xiao Yi is a foolish, childish & innocent girl. He is her boss & she is his secretary. He bullies her yet at the same time will not hestitate to protect & shelter her. Thus, she can always rely on him. Their relationship is a funny one on how opposite attracts.

Li Wei Ran (5th brother) & Qin Sang – Li Wei Ran and his cousin Qin Song fell in long with Sang Sang who is An Xiao Yi’s best friend. Sang Sang sees Li Wei Ran as a good man. He is polite, patient and passionate whereas she is independent, intelligent and interesting. They are a perfect pair but she is afraid to love so he has to work hard to convince her he is worthy of her love..

Short sequel on their children.

In the foreign world, the martial artists dominate the world and the sword of the emperor controls the fate of hundreds of millions of lives! Long Yu, the number one killer on Earth, after dying, takes rebirth in this new world in an aristocratic family of martial artists but faces rejection because he is unable to practice martial arts.

- Description from Novelupdates

Yu Youyao had a nightmare. In her dream, she was married to the Marquis’ son, Song Mingzhao, and had become a mere medicine-human for her third sister, Yu Jianjia. After having blood extracted from her heart for three years, Yu Youyao’s life was nearing its end, so her wrist was slit and she died just like that.

Upon waking up, her heart thumped wildly and she decided to choose the first man she saw to escape that tragic fate. Thus, she clung onto the leg of her maternal cousin who had come all the way from the You Kingdom. “Cousin, I’ll be good to you for the rest of my life.”

Zhou Linghuai looked at the girl nestled in his arms. She had a lovely face and puppy eyes. Despite his usual ruthlessness, he suddenly found himself unable to reject her. And so, he became Yu Youyao’s protector, helping her to take revenge on those who bullied her, fend off the schemes of others, and reject all of her suitors. He even helped her attain glory and magnificence.

Once Yu Youyao reached adulthood, events started to progress according to her dream. The Marquis’s son, Song Mingzhao, had indeed come to request for her hand in marriage. However, Zhou Linghuai pressed Yu Youyao against the wall and said in a low voice, “You’re mine. You can’t marry anyone else!”

Xiao Ze, who was dedicated to the people and vowed to become a generation of Ming Jun, accidentally fell on a little lady.
The little lady was born beautiful and lovable.
So Xiao Ze accepted his life and got the name of fear.

ps:
①The male protagonist has no concubine, and he is dedicated to serving the country.

- Description from novelbuddy