Hello, Hero Candidates!
Thank you for playing the Devil Book.
To increase the Hero's grade, the hero's Soulstone is necessary.
But when you get a higher grade Hero than the current Hero in the Summon, our system raises the character's grade immediately instead of giving Hero's Soulstone for the convenience of users.
Check the difference between the amount of the Soulstones needed to raise the grade and the amount of Soulstone you get when you summon a hero you already have.
For additional inquiries, please email at firstname.lastname@example.org