The Tycoon's Enchanted Mermaid - Chapter 144: Playtime

As a promise, he went out into the world as an assassin. 3 years later, after becoming the Supreme Assassin, he gave up on everything he had and returned to the ranks of ordinary people. But one day, Kismet, a mystical game created by the National Research and Development had appeared.

Enigmatic hands, spectral frame, and one cunning strike just like the swing of the Grim Reaper. The Supreme Assassin takes on the mystical world, and how his legendary tales sets off, progressively ascending the altar to becoming the best.

- Description from Novelupdates

Xu Youyou rebirthed to when she was 16 years old and chose a path different from her previous life and met Qiao Mu ten years earlier. The youth who had braved the wind and snow protecting her till death — and who had confessed to her.

And she realized, the Qiao Mu ten years earlier and the Qiao Mu she knew were completely different people. He didn’t have his smile that could radiate sunlight, he didn’t have his courage that could penetrate snowstorms, and he certainly didn’t have his perfect eight pack. He was like a short mushroom, quietly growing in the corner’s shadow.

Xu Youyou: If you dare be like this when you confess to me, you are so dead.

Qiao Mu was a teenage Weiqi genius, he loved Weiqi, but because of his shadow of youth was unable to enter the competition arena. And because of the fear, he was unable to become a professional player and could only return to a typical school life.

Until he met Xu Youyou.

A widely known reckless and fearless girl, who was the complete opposite of him. She was good at everything, except things relating to love. Clearly he wasn’t her type, yet she always provoked him. But the biggest joke was himself, he clearly knew everything, yet could not help but fall into the hands of the enemy.

- Description from Novelupdates

A girl who calls herself a demon appeared before a timid student named Fumio Kijima. The girl claims to be a campaign girl from the demon world and she gives him the ability to “summon a room” from nothing but thin air.

At first he doesn’t abuse his power and uses it as a convenient ability in his every day life. But one day he is bullied by his classmates under a false pretext and is made to suffer. In the past he would have wallowed in misery and cried himself to sleep, but now he had a power to call upon.

“I will make them regret it!”

Using his powers to summon his “room”, he begins his era of confinement and brainwashing to achieve his goals.