This is the fifth entry in the "Night High" series.
Classroom after school. You find yourself standing alone and realize that you have a strange app on your smartphone. Then, class representative Rei Saionji comes in to lock the door.
A somewhat famous online streamer. They have a mentally unstable disposition and a desire for death, constantly saying they want to "die beautifully." Claiming to host a "suicide stream," they visit the Sea of Trees, but what awaits them there is a horrific ryona trap dungeon far more terrifying than death.
Just as peace was beginning to return to the world after the defeat of the Demon King, a shocking event shook the globe.