Hi. I'm not sure about some words used on the game. But I hope it will help.
1. premium item is a special item which can be bought by 'gem of temptation' alone.(also available with a box containing 'gem of temptation')
2. 3 kinds of premium items are exist which are 'decorative item', 'special portion', and 'functional item'.
3. lasting of premium item can be shown by clicking 'preminum item icon' on the bottom-right corner of the screen.(shortcut 'J')
(it shows valid time of item 'wisdom of wise man' and 'stone of wise man')
4. each time, you can use only one premium item with a time limit.
5. premium item can be bought from Kaduru in Kwanato and Armo in Temose.
6. you can not resell premium item at the shop.
7. you can not throw out premium item on the ground.
8. you can not resell or throw out any special portions except 'pira' and 'spon' because of recent addition of 'premium item'.