I should have posted this before the chapters as well oops.  

Monster/Magic beast rankings.

F-rank: Threat to one or more people 

D-rank: Threat to a small party of mercenaries 

C-rank: Threat to a veteran party of mercenaries

B-rank: Threat to a town

A-rank: Threat to a kingdom

S-rank: Threat to a continent 

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Mercenary rankings. 

F-rank: Newbie/ Strong as your average townsperson 

D-rank: Amateur/ Stronger than your average person 

C-rank: Veteran/ Able to take out medium size monsters/magic beasts 

B-rank: Well known/ Able to take on stronger, bigger monsters/magic beasts 

A-rank: Powerhouse/ Able to take out multiple powerful monsters 

S-rank: Legend/ Able to take out S-rank monsters/magic beasts 

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Adventurer ranking. 

F-rank: Newbie/ Only capable of scouting small areas 

D-rank: Amateur/ Capable of scouting medium areas 

C-rank: Veteran/ Capable of scouting large areas 

B-rank: Well known/ Capable of scouting medium areas while hunting small low-rank monsters/magic beasts

A-rank: Spy/ Capable of spying on other countries 

S-rank: Legend/ Capable of scouting large areas while hunting high-medium rank monsters/magic beasts 

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Thank you jokei for pointing out the problem of countries and kingdoms.