Under the Oak Tree (Web Novel KR) - Chapter 262

In this life, I will live for you.

Kai of the Sorcerer’s Tower is one of the last mages left, barely surviving in a world ruled by creatures of the dark — where the era of mages ended, and most of the lands got contaminated with dead mana. To save his world and fulfil his master’s last wish, he put himself through a forbidden ritual, risking his soul being ripped into pieces to make his way into the past. In an era with abundant mana — an era yet to enter the Golden Era of Magic. Things go wrong, of course, as they always do, and he finds himself thousands of years before the world fell to mana contamination — in the body of a young lord, Arzan. All is not well, though, as the young lord was murdered by someone right at the cusp of a beast wave threatening the territory, while larger threats loom on the horizon. There was a lot to do for Kai to regain his former strength in this time of primitive technology, but then again, he might just be able to change that.

The mentally disabled 13 year old daughter of the Ye family, one day re-births! She rules over the Omnipotent God’s Cauldron, she possesses a spirit cultivation space. She’s no longer the good-for-nothing, abandoned girl who everyone bullies whenever they see her! With her incomparable poisons, even miracle doctors have to move to the side.

Spirit beasts beg for contracts, but too bad, even the God of Beasts have to call her Boss. Scum father, you dare to abandon your wife and daughter, she will surely make him destitute and homeless. People of the world, you dare to bully her, to insult her, she will definitely pay them back a hundredfold.

Reborn again into the world, she returns as a sovereign, but who knew she would attract the nefarious-blood-thirsty-demon him. He’s definitely the sly emperor who doesn’t hesitate to kill and cut down anyone, but he transforms into a harmless foolishly cute prisoner prince of an enemy country……

- Description from novelupdates

Time travelling from the majestic era after the Recuperation of Reiki, he became Kimura Kazuki, a 16-year-old high school student in Japan, one year before the Reiki Recuperation.

Tentatively, he set out to hone himself to the bone, burning candles at both ends to stockpile resources in preparation for the imminent Recuperation of Reiki. His goal was to be many steps ahead of all humanity when the time comes.

However, it seemed like fate had decided to play a cruel trick on him.

One year later, the Recuperation of Reiki… did not happen as expected.

- Description from Novelupdates