Classified Employment Contracts (CEC) are a type of currency in COUNTER:SIDE used specifically for the recruitment of Awakened units. If you’ve played E7, the system is analogous to mythic summons and moonlight heroes.
1. Event - get more rewards
2. Main - to open upper contents
3. Side Story - until you get all side only characters
4. Supply - when you did all 1~3 but you have Eterniums left (check more details below)
This [Counter:Side] Guide is based on the current META on SEA server of the game, which is 1.5 years behind KR version and 6 months behind TW. Since we don't have access to many characters, whose best at what will differ. But please note, it's not worth chasing an unit that's good now, but will become meh later down the line