Brave Story: New Traveler

-Firewyrm Soul: Find Toni Fanlon at the inn in Lyris. He has two sidequests for you. At the beginning of the second one, he asks you for the Firewyrm soul. If you give it to him, he will reward you with the Heaven Bracelet and Spirit Diagram 3.

-Demon King's Soul: After completing the quest mentioned above, show Toni the Demon King's Soul. He will tell you to go and show it to his master. Travel to the cabin northeast of Paulta Mines, and show the soul to the old man (Steel Will) inside. Your reward will be a Hell Amulet.

-Captive Soul: Steel Will's last quest is actually that he wants to see the captive soul. Complete his other quests first, then show him the soul to get a Hell Choker weapon.

Check the FAQ made by Misfit119 in the FAQs section. Search for "Book Of Quest". Those item are actually needed in some sidequest which will grant you special item. Check the requirement for each quest though ..... since some of it are chained quest.

Some [extra super acropyredynamic] minor corrections for snkupo's answer:

When Toni asks you to give him the Firewyrm Soul, he will reward you with Heaven Bracelet only. After that, you should give him the luckmagnet for him to give you the spirit diagram 3 and Heaven Ring. Then talk to him again and show Toni the DK's Soul. "He will tell you to go and show it to his master. Travel to the cabin northWEST of Paulta Mines, and show the soul to the old man (Steel Will) inside. Your reward will be a Hell Amulet."