Thanks to multiple Yanfly plugins, I have made a system of advancement for weapons in my game that I have called, "The Power Core System." I'm sure something similar has already been done but I wouldn't know about it, so I still kinda came up with it on my own. XD Anyway, let's get into the nitty gritty.
First, let's talk about the basics. To start with it, you're gonna have to defeat enemies. Every enemy in my game is gonna have an element associated with it. Even ones that don't, which will be considered "Neutral" elemental. All monsters drop a resources associated with their element, and in 3 different kinds. Shards, the most common, usually dropped by common and weak monsters, Gems, a rarer kind, dropped by uncommon and stronger monsters, and Crystals, the rarest kind, dropped by the strongest and rarest monsters. There's also Attack and Defense ones, which will be buyable and stores. After you've gained enough, you move on to crafting with them.
You can usually use the shards by themselves to make cores of the elements, making Elemental Cores. But you can also find special combinations that will give special effects, such as Quake and Wave elemental stones making Poison Effect Cores, or increasing stats depending on the stones, such as Flame and Quake giving an attack boost. The kind of core it makes will also depend on the type of Attack or Defense stone used, but that's yet to be implimented in this build.
Finally, you equip them onto the weapon of choice, changing it in certain ways depending on the core. It ends up gaining an element, status effect, and/or stat increases depending on the kind. This will make grinding double rewarding, because as your gaining EXP, you'll also be gaining resources to make new Cores.
Armor has their own setup. While weapons give elemental properties and status effects, armor will defend against those. The kind of core you get will depend on whether you used Attack, or Defense stones in the crafting. This is simply a rough draft of the system as well, so it may change down the road depending on feed back.