From the background Esper influences all living things and that most beings have a particular affinity to a type or 'colour'.
There are six types of Esper and a units affinity is represented by the colour of their Faction symbol on their card.
How does Esper work in game?
Each player has a deck of 42 Esper Cards. It's a standard deck so not like other games where you can build a custom deck. But it does come free in the Faction Battle Boxes (essentially one player starter cadres).
Most cards have a big Esper icon (primary Esper type) and a small Esper icon (secondary Esper type). These are called Standard Esper cards and can be played as either 2 Esper of the Primary or 1 Esper of the Secondary.
The other two card types are VOID cards (the big black circle that looks like a solar eclipse) and WILD cards (the card with all 6 Esper icons). Void cards are worth 0 Esper and just take up space but the Wild cards can be played as 1 of any Esper (choose when you play it).
At the start of the game each player draws a hand of 5 Esper cards from their own deck, this is kept secret from your opponent and only revealed when they are used. When Esper cards are played they are placed on a discard pile. If/when you draw through your deck you just shuffle the discard deck and start drawing from this.
So now we have the cards what do we do with them? Each of our models has a stat/tracker card that tells us how good they are at certain things (ranged attacks, defence, movement etc) we'll discuss these cards at a later date. These cards will tell us what abilities we have and what they cost to activate, the cost will be listed by coloured icons and a quantity. We need to pay this cost from our hand to activate the ability. Let's say I'm making a ranged attack with a Green 2 and a Blue 1 - that's what I need to pay to be able to make the ranged attack.
When you choose to use an ability you will have a value on your stat card. For now let's say I'm making a ranged attack and it has a value of 2. This allows you to immediately draw 2 new Esper cards and add it to your hand.
Next benefit of Esper is activating 'Presses'. A Press is a bonus to the standard ability and has an additional damage or in game effects. The Presses are detailed on a models Reference card and have an additional cost.
At the end of your turn you may discard any and all cards from your hand and immeadetly draw back up to 5. If you end the turn with more than 5 cards you must discard down to 5. Perfect time to get rid of those Void cards!
Most units can store 'Held Esper' some can even generate it when they activate or by taking the 'Refocus' action. If a unit can store Esper it will have a number of white circles on their card you can mark. When they wish to spend this held Esper they can use it as 2 of any single colour.
A Cypher is like a pet that is bonded to your Knight (leader/hero). They are pretty much immune to attacks. Their main purpose (it seems) is to generate and transfer Esper. If the Knight can draw line of sight to his/her Cypher they can add 1 held Esper.
Other uses of Esper
There are a set of cards that list General Actions for each Faction type which may be performed by Initiates and Masters of that type.
You can use Held Esper to heal objectives.
Probably others... Will keep reading and learning! ;)
So what does this all mean?
This Esper mechanic means you really need to plan ahead and consider what units you will be activating next. If you've lucked out and not drawn the right cards you need yo think of an alternative strategy. Also maybe consider what Esper you might need for defensive abilities before discarding and redrawing.
The ability to generate and transfer held Esper shouldn't be overlooked either as this provides a huge amount of flexibility. But watch out for those Esper Thieves!