This system is made for Akashi and Akashi Kai. Now if you have her as your secretary ship, you will be able to use the Arsenal.(Tip: Hover over the factory icon to get in there)
To use this new factory, you need Improvement Materials. You can get them from Quest, or exchange them w/ medals, some new quests will have their reward as Improvement Materials. Also, you can buy those Improvement Materials from the in-game cash shop, the price is 700 DMM points for 10 Materials.
To improve your current equipment, you will need resources, development materials and Improvement Materials. The equipment that has been improved will have a ★ beside them. If the improvement level is low, then you will have a higher chance of success, and vice versa.
If you reach the maximum improvement level of your equipment, you can Improve your equipment into a better, and a higher ranked one. However, your improvement level will be wiped once you do this. Also, if the new equipment after improvement is something you can develop from the normal factory, the improvement level will automatically be +3.
Tip from Official Twitter: For everyday in the week, the equipment you can improve will differ.
And, when Akashi is at your first slot, some certain kanmusu will bring changes to the equipment you can improve. (Yes, certain, need more info here)