You will need to use your (beginner) blackstone weapon and (begginer) blackstone armor (item) to re-purchase your naru set. You can only do this on a season character. You can get begginer blackstone weapon and armor by questing and by completing some tasks in the season challenge log. To exchange them you must speak with Fughar. If you completely got rid of all of your beginner blackstone weapon and beginner blackstone armor, you can use heating on Blackstone weapon or blackstone armor to get more.

When you hover your mouse of the items it will give you contextual description of the item, its use and how to obtain more of. In general you can get thousands of them when you complete your main story quest and seasonal challenge log so be sure not to use failstacks while enhancing or crons. You can "YOLO" enhance until it becomes Tuvala. To enhance seasonal gear I would recommend a dedicated guide for it.