Weapon Upgrade Rules
The sources describe story and crafting prerequisites for weapon enhancement, permanent crafted upgrades, and temporary upgrades that last for one dive.
How it works
IGN says upgrading weapons through Duff’s shop requires reaching Chapter 2 and receiving his request to acquire materials. VG247 says the Weapon App unlocks after the Weaponsmith Duff side quest and describes further enhancement after later story progress, including defeating the Giant Squid and building the translator. It says a weapon must first be crafted in the app. IGN distinguishes permanent upgrades from weapon-cache upgrades that raise a gun once for the duration of that dive.
Read the supporting references
A source-bounded reference to reported diving gear effects and named weapon upgrade paths, including prerequisites and progression rules. Staff skills and restaurant upgrade effects are outside the retrieved evidence. Guidance explains the referenced mechanics; it is not a tested damage ranking. Check the stated edition and source version before applying a patch-specific detail.