Protagonist and Crew attributes begin to matter as you level up. Developing them will benefit the particular member.
Each crew has a particular attribute that will enormously increase its primary stat. In the picture, for example, is Blackbeard Pirates' navigator, Laffitte. His effectiveness relies on Intelligence. As his intelligence increases, his special skill, Funeral, increases in damage. This is a feature of a special skill apart from Intelligence increasing Magic Attack.
Strength increases Physical Attack and Physical Defense
Intelligence increases Magic Attack and Magic Defense
Physique increases HP
Agility increases Speed
There are two options in developing an attribute. One is consuming Prestige (earned by fighting) and consuming Gold (earned by completing fights and by buying with real money).
Prestige is being consumed in this image. Notice that there are greens and a red one. A green color and an arrow pointing up is telling that this particular stat will increase when Replace is clicked. A red color and an arrow pointing down is telling that this particular stat will decrease when Replace is clicked. We want Laffitte's intelligence to increase, so we will click Maintain here. As an attribute increases, the harder it gets to increase it further.
This will not be easy. Apart from this testing our patience it is also very tiring and can get painful to our hand. I suggest using the keypad as a mouse. Press Alt+left Shift+NumLock to enable keyboard mouse.
Key 5 is for left clicking
Key 4 is for moving left
Key 6 is for moving right
Key 2 is for moving down
Key 8 is for moving up
The mouse is still active even while using the keyboard mouse. In order to disable, just press Alt+left Shift+NumLock again.
Have a happy adventure!