I'm not sure specifically what the 'Resin Game Story' is about as it could be a very unique or niche concept. It might be a story related to resin crafting, like perhaps a tale about creating art with resin. Maybe it involves characters who use resin in some sort of game - like a crafting competition or something similar.
Maybe the main characters in the 'Resin Game Story' are a group of adventurers. They might be exploring an area rich in resin resources. Or it could be a family of craftsmen who have a long - standing tradition of working with resin and their story is about passing on this knowledge and craft within the family while also dealing with the challenges that come with the resin game or resin - related business.
Nezuko is initially 12 years old in the manga. As the story unfolds, her age doesn't change significantly in a traditional sense, but her character development is quite remarkable.