User blog comment:Darknessabove/The explorer, volume 1, chapter 2: friend or foe?/@comment-25359858-20141114200120/@comment-25421410-20141114230730

Well E would be the lowest, which would comprise of humans that have some how escaped after being captured by monsters, which would go up to A which would be humans that have killed monsters or stolen from them multiple times while causing unnessary damage.

Rank S is where shit gets real, these are usually allocated to heros, who due to being blessed, can easily slaughter monsters or threaten the safty of monster villages.

This goes up to Rank SSS, which is reserved for those that could potencailly kill the demon lord, which is equal to being able to challenge a god.

S ranks are where monsters may be inclined to kill the person with the bounty on their head, though it can vary based on what they are wanted for, For ones like Garth, that have not been reported to of killed any monsters, hes seen as a very valuable and challenging target to make their husband, part of the reward on his head is actually in it self, a way for them to capture the heart of that man.

This is more a quick version, i'll have to think on what comprises each rank, which i'll probally think of tommorrow after work.