I don't know what goes in this case but I would not commonly expect defence values to be in a save game. Looking at the save editor the shields have the optional ability to have an increased surf or shield guard (possibly even two levels) as a kind of perk but straight defence is not an option.
Normally games have a table of stats in the game itself and reference that, any saves are just to note what and how many numbers of said items you have.
It is not impossible for it to be in a save and there are plenty of gameplay reasons to do such a thing (randomly generated weapons for one) but seemingly not here.
To that end you will have to drill down into the game and figure out where it is within it, or maybe as a cheat if it copies that value to RAM and references that. On an older system with a nice debug emulator it makes for a nice getting to know hacking project, for a modern device without much debug capability and emulators not being that much better... yeah it can be done but if this is your first crack at ROM hacking then you are in for a hard time.