Sickness unto Love novel

More than 150 deaths across Japan have been linked to Blue Morpho, a game of escalating tasks ultimately leading to suicide. The mastermind behind it is Kei Yosuga, a high schooler admired by everyone around her. Kei’s childhood friend, Nozomu Miyamine, knows this all started with one murder that would change both of their fates forever, but still, he wonders how this incredible girl could have become such a monster. Yet if there is one thing Nozomu knows, it is this: He will never stop loving her.