ECA is one of the satellite organisations created around MSB. Its primary goal is to locate, analyse and eradicate (if necessary) Ephirite manifestations. When a Dryad materialises in a central park and starts healing people, ECA marks her as 'useful specimen, threat level 0' and lets her to continue her good job. But when a fantasy troll berserker appears in the suburb area, ECA sends an agent or a storm group to deal with the aggressive creature using Null-guns and other specialised equipment.
ECA is a relatively small agency, partially due to the fact that the entrance exam for an agent is very unusual, which fends off many willing candidates. It goes in a form of a deep mental scan performed by a level 3 or higher telepath from MSB (it's like FBI+KGB on steroids). The big amount of aspirants can be explained by the fact that ECA gained a lot of influence and political weight in less than two years of its existence, plus big salary, insurance (including lost limbs free replacement), cool toys and 'aura of authority' that surrounds every agent. There is a possibility to get a transfer from ECA to MSB, if you'll live long enough and get impressive enough record to earn it. Usually ECA gets its agents from SOB (police), Church Patrol or (in rare cases) Templars. ECA officials don't like to work with ex-military candidates due to frequent cases of dormant psychological traumas and lack of detective skills.
One may think that ECA is nothing more than another SWAT team, but it is far from truth. The main goal of ECA agents is to investigate, find and eliminate dangerous Ephirite creatures which have a form of a normal human. Animated skeletons? Trolls? Garadr has Church Patrol and Templars for that. But When a vampire appears in the city, or a den of werewolves must be found - officials call for ECA. Its agents have a permit to eliminate any Ephirite life form above danger level 3 on sight without any additional 'court permissions' and other before-the-war crap. They can also mark a creature as 'useful' or 'friendly', but it usually happens only after the White Breakthroughs, when White Ephirite takes form of a good fictional creatures, angels or other positive and non-harmful beings. But the main ECA clients are 'Shifters' - Ephirite-poisoned citizens who started to change and conceal that fact from MSB and other agencies. Shifters after Stage 4 changes are officially declared non-humans by the officials. Post-4 shifter loses all his or her civil rights and becomes a fair game for ECA and MSB agents.
SOB is very jealous because ECA receives the latest tech toys, the biggest budget and a closer attention of the media. That's why there's a tension between those two branches, when SOB thinks of ECA as of 'arrogant arseholes', and ECA thinks of SOB as of 'idiots who slow down our work on purpose'. Usually a single message from MSB curator momentarily ceases all those 'misunderstandings'.
ECA receives most of its tech from MSB, which allows it to have equipment SOB can only dream about. The list includes pocket lie detectors, compact respirators, deployable force fields, central data system-connected glasses with advanced reality function, concealed special weaponry, MSB-grade Null-guns and many more. The uniform of an ECA agent is represented by a special armoured trench coat, which is based on MSB design. It can withstand direct fireball hit and protects its user from bites and small-calibre projectiles. ECA model is not that armoured and technically-advanced as MSB one, but it still provides its user with great protection. Those trench coats even have an in-built temperature regulation system, plus some other minor systems like a GPS beacon and such. But there are limits to MSB generosity. For example, ECA has no right to use E-transport (anti-gravity vehicles), or, for example, it can use Tank Suits only after getting permission from MSB higher-ups.
Usually ECA agents work alone or in pairs. Squads are gathered only if a big threat is detected, and Church Patrol, Templars or MSB is too far away to get there in time. So, unlike MSB four-men elimination squads, ECA storm squads see almost no action. Another reason for a 'loner' behaviour is that ECA agents are investigators rather than storm troopers. They are trained in the field of E-creatures elimination, but their main goal is to detect, locate and determine the threat level of a creature or a shifter. But this is only on paper. Usually the agent who finds a dangerous E-creature attacks it on-sight. One of the reasons for such behaviour is a bounty, which officials pay to every agent who eliminates a dangerous E-creature. This created some rumours about 'dirty agents' who deliberately inject shifters with 'black' Ephirite to get more 'kills' and, in turn, money. (that's why 'The Eye' program was started, attaching a recording device to every agent) That's why some people call ECA agents 'killers' or 'cut-throats'. The general reputation of ECA is on 'necessary evil' level. No one really likes them, right until the moment when a vampire starts a slaughter in a mall. After that - 'ECA, help!' And ECA agent goes in, grumbling 'F*cking civilians...' in the process.