Note: Demon Ranks do not work exactly like Hunter Ranks but what you see below is the best approximation
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Human Ranks (Just basic representation),
F Rank - Lvl 1 to 5
E Rank - Lvl 6 to 10
D Rank - Lvl 11 to 15
C Rank - Lvl 16- 20
B Rank - Lvl 21 - 25
A Rank - Lvl 26 - 30
S Rank - Lvl 31 - 34
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Demon Ranks (Note - Demons do not evaluate ranks based on level but strength and capability. So if a Lvl 4 were to beat a Soul Warrior, then his rank will become Soul Warrior),
Soul Eater - Lvl 1 to 5 (Just to give an idea)
Soul Warrior - Lvl 6 to 10
Soul Slayer - Lvl 11 to 15
Soul Hunter - Lvl 16 - 20
Soul Reaper - Lvl 21 - 25
Soul Purger - Lvl 26 - 30
Soul Devourer - Lvl 31 - 34