The students of Kamishiro High-School Class 2-A swore revenge on their homeroom teacher, Takao Nanami. Against her, a fake suicide had been concerted, meant to be played out by one of her students, whose actual death would later sink the class into confusion. Who soiled the water with blood? Skinned of its trust, their friendship became an urge to sate each other’s hunger.

(Source: MU)

From MyPersonal-scan/Tcmanga:

A mysterious command arrives from a "King"-----
The life-threatening "Game" has now begun for the 32 students of the first year's B Class.

One day, all of the students in Nobuaki's class received their first message from someone calling themselves the "King", in which was written a baffling command.
That first command was very easy. However, the commands began to escalate until a life-threatening game had begun---

Failing to obey the orders leads to death!! Their friendships are being undermined by a bottomless terror!!

The winner of the first edition of the King's Game is transferred to a new school. After being initially afraid to make new friends, traumatized by his experience in the past, he starts to forget the King's Game and sympathize with his new friends. That's when the new King's Game starts...
(Source: MAL)

"The King's orders are absolute. Fail to obey, and you will be punished."
30 years ago in the remote Yonaki Village, a black envelope is delivered to a single villager. The command inside threatens to draw the entire population into a terrible tragedy!
Take a deep breath, steady your heart, and prepare for a shocking, terrifying survival horror adventure! The latest chapter in the wildly popular "King's Game: Origin" saga has begun. It all starts here!
The prequel of Ou-sama Game (RENDA Hitori)