My Mother Has a System but Won't Use It - Cultivation System [Minor Spoiler, read with caution]

He is a young man without a spirit root. It is believed that this denies him the chance at cultivation. However, a mysterious lady imparts a Supreme Demon Classic to him and from then on, he starts his path of cultivation.
He undergoes a total transformation to emerge as the most fearsome and powerful fiendish demon in his era, that even immortals and fiends are fearful of him, and saints are at his beck and call.
Mastering the Supreme Demon Classic is the turning point in his life. He is able to unleash his immense and divine power from within, illuminating the entire universe!

- Description from Novelupdates

On the distant Tianxiu Planet, there exists a group of unusual and intelligent beings. They consist of neither children nor elders. They have neither birth nor real death. They are born into the world through an extremely special process and have managed to keep their fundamental memories of survival through their endless reincarnations.

They are the Tianxiu people.

For every Tianxiu person, if they find someone they like and want to bind as partners with each other — then they would have to go through a life or death Adult Ceremony. The winner of the ceremony will become the absolute dominant in this spousal relationship.

While the defeated one will be referred to as — Qizi.

- Description from Novelupdates

The daughter of a duke, the stuttering Maximilian, married a knight of lowly status at her father’s coercion.

One day, I – a high schooler – found a paperback in the hospital. The “Disease Coexistence Journal” was its title. It was a diary that my classmate, Sakura Yamauchi, had written in secret. Inside, it was written that due to her pancreatic disease, her days were numbered. And thus, I coincidentally went from Just-a-Classmate to a Secret-Knowing-Classmate. It was as if I were being drawn to her, who was my polar opposite. However, the world presented the girl that was already suffering from an illness with an equally cruel reality…

The best-selling, award-winning debut work by Yoru Sumino:

“Bestsellers 2016 (Overall) by NIPPAN” – 4th Place

“Bestsellers 2016 (Paperback Fiction) by NIPPAN” – 1st Place

“Bestsellers 2016 (Overall) by TOHAN” – 5th Place

“Bestsellers 2016 (Literary Books) by TOHAN” – 1st Place

“Bookstore Grand Prix 2016” – 2nd Place

“DA VINCI BOOK OF THE YEAR 2015” – 2nd Place

“Bestsellers 2015 (Literary Books) by TOHAN” – 6th Place

As of May 2017, this book has sold over 1.2 million copies.