After the killing game began, Monomi began to panic, because the simulation was designed to be peaceful and there was no procedure for dealing with that kind of scenario other than shutting the simulation down.Monokuma forced her to attend Class Trials despite her revulsion, tying her up with rope and suspending her from the ceiling.Both Chiaki and Monomi accepted their fate for the sake of the surviving students, willing them all to not give up on their futures.They were both executed in a punishment themed around Chiaki's talent of Ultimate Gamer, called Please Insert Coin.Nagito set a trap, knowing that due to his talent as the Ultimate Lucky Student, it was guaranteed that the traitor would unknowingly throw a poisoned fire extinguisher canister which ultimately killed him.
As a final act in defense of the students, Monomi decided to sacrifice herself, grabbing hold of Monokuma and self-destructing.
Usami tried to defend her students, but Monokuma overpowered her and used the virus to strip away Usami's "magical" abilities, changed her appearance to resemble his own, and renamed her Monomi.
He then demonstrated his power by "executing" her using his Monobeasts, a team of large animal-shaped mechs with oversized weapons, although Monomi was able to respawn due to having spare copies.
However, when Nagito became increasingly more determined to flush out the traitor among them, he broke into Monomi's House and stole her treasure box.
Inside the box was a diary of the events on the island, written and illustrated by Chiaki.
A second Observer, in this case, an avatar of Chiaki Nanami, was also created, based on one of the students' classmates who had been killed.