Was it Good? - Boktai: The Sun Is in Your Hand | (GBA) Gameplay
The game's story takes place in a time period near the end of the world, called the Age of Darkness. The story features the appearance of undead creatures after the natural cycle of life and death was broken. People quickly began dying due to the use and misuse of "Dark Matter", a type of energy that corrupts and destroys life. Those who survived quickly became prey to dark creatures called "Immortals", beings composed of Dark Matter at the cellular level.
The story is set in the city of Istrakan, which had already been overrun by the Immortals. The city was in a hopeless situation as the curse brought the "undeadening" of all, edging the human race closer to extinction. Even the heroes who used to hunt the Immortals have already fallen, and so people's hopes have been shattered.