Some characters in the game once obtained have special items. some are significant like Arngrim's Dragon Slayer. Some are as useless as Lleweyn's goddess pendant. Here is a list on some that you can obtain:

Arngrim- Return to his bedroom to obtain the Dragon Slayer
Janus- Return to his home to receive the raven slayer
Belenus- Enter Asaka's bedroom to obtain the crushed flower
Mystina- enter her room to get the Infinity rod
Kashell- to obtain his sword return to the Camille cemetary.
Badrach- talk to the little girl in the Camille church to obtain the woven bandana
Yumei- return to the beach at Hai Lan to get the cerulean lapis
Nanami- enter the Dragon God's palace and return to the shrine she met Minayo at to receive the DragonBane sword
Lleweyn- Return to the forest where he last hugged his girlfriend to recieve the Goddess pendant.