Kyoukai Senjou no Horizon - Volume 8A, Chapter 4: Noticer at the Preparation Ground

After seeking pleasure in the nightclub and a night of romance, he discovered there’s a seed in his stomach;

It begins on the mountain.

With the glint of a knife, a flash of steel in the hands of a sworn brother. A betrayal.

Stabbed and pushed down the mountain, Zi Chen lied within the red-stained snow, left to die.

This is where it begins; he is given life by lightning,
baptized by thunder.

Those who had once betrayed him should all suffer in his cruel revenge.

- Description from Novelupdates

Zhangsun Zijun and Yi Xichen are the protagonists of the novel “Record of Nine Thousand Vicissitudes.” One is solid and reserved; the other is free-spirited and uninhibited. As fellow disciples under the same master who grew up together, the two have a deep friendship that was strengthened by their numerous life and death adventures together.

However, in a popular yaoi fanfiction, the personalities of these two characters is completely OOC. Zhangsun Zijun turned into an insanely jealous, insatiable s*x addict madly in love with his wife Yi Xichen. Yi Xichen turned into a sweet, delicate little angel. Their daily life was full of kinky bedroom activities…

Suddenly, the Zhangsun Zijun character from the fanfiction was transported into the world of the original novel.

- Description from Novelupdates