Fantasia: The Realm of Thanos

"Please save Fantasia!" a woman asked you. She's in front of you, a lonely girl who does not have anyone, asking you to save an unknown world from doom by obtaining a heart key from one of four "strong boys". You decide to do the task, but...... The first one is a Demon Lord.... The second is a bloodthirsty assassin... The third is a mysterious hooded guy... And the fourth... has curse placed on him... To obtain the key, there are those who will try to stop you, a shy maid, a happy-go-lucky elf, a lonely demon, and also the bearer of the ultimate key... ...Oswald Leingold.