The C-Class is, within the ranking system of the G.O.T.T and G.T.O, the third strongest class and only the rare, and commonly unknown G-Class and the S-Class are above it in the ranking system. Because the G-Class is rather unknown, it's generally assumed that only the S-Class is above the C-Class.
Members of the E.S that possess a C-Class ability are ranked as C-Class members and are usually sent on dangerous missions, which could, and most likely would kill non-E.S members, and to missions that are highly sensitive and political.
Because of their rank C-Class members, within the G.O.T.T and G.T.O at least, can only be ordered by either their Chief or G-Class and S-Class E.S members. It is possible for them to order members of other Units, like the S.O, because of their rank as E.S members. The C in C-Class stands for Channel Opener.
C-Class abilities can be subdivided into the Categories: Offensive, Defensive, Information Gathering and Support abilities, though it isn't unusual for one ability to fit into more than one category.
Offensive abilities are abilities that are actively used for combat to bring harm to an opponent. They're actively used to infect damage on one opponent.
Their range can differ from short range, to mid range to range.
Defensive abilities are abilities also abilities for direct combat, but unlike offensive abilities, these deal with defence instead of actively trying to inflict damage on an opponent.
They can vary in their protective area. Some can only be used to protect the user themselves, while others can be used to shield much more people.
Information Gathering abilities are passive abilities that are mostly unsuited for battle. They're primarily used to gather information on an opponent or target. Which kind of information is gathered varies from ability to ability.
Support abilities are mostly passive abilities. They deal with healing comrades after a battle, strengthening them or even bring them to safety.