Valkyrie: Card 1

Before heading to battle you need to choose your valkyries who will fight for you. To get there you need to tap on Edit Unit.

Do you see the card cost above the slots? The card cost tells you  how many cards you can have in one unit. And also you should have a maximum of 5 card slots, if you only have 3 then i suggest read Valkyrie: Expansion 2

Here's an example of how it works. Check that Hiderigami card, it's unit cost is 62. whenever you place a card to a slot you will be able to see the total card cost of all equipped cards on that Unit which is shown on the left unit cost while the maximum card slot on the right and you can't put in more than what's on right. This will probably limit you on adding those good cards that you have, if that is your case then I suggest to read on Valkyrie: Expansion 2 to see how you can increase your unit cost besides leveling.

See the units here, you'll have 4 Unit at your disposal. 3 units for attack and 1 for defense. What we do here is we seperate the cards from their purpose. What you see on Attack unit 1 are cards that do critical damage and buffers of attack damage stat. This unit is for subduing an archwitch here you need cards that can do more damage, Valkyries here are those that can land one good hit on the archwitch. The attack unit 2 is where I put all Valkyrie cards that can do Aoe or damage to all, because this unit is for campaign where you would want one card that can annhilates all enemy cards in one turn for faster advancing and lesser damage to your unit less cost as well for recovery. While I keep the Attack unit 3 for duels. Your Valkyrie cards on your Defense unit are the ones being attacked whenever there is an Alliance battle.

Here are the rankings of Valkyrie cards.

UR card is the highest rank among Valkyrie cards and most formidable when awakend. Once you combine UR cards it will give you a HUR card while awakened cards are GUR.

SR card is the second highest card rank these cards can turn the tide on every battle. The same with UR you can combine it with other SR cards then it will give you HSR and GSR when awakened.

N and R cards are  the most common card you can get and when combined it gives you HN and HR cards. These cards are use for leveling and boosting stats of UR and SR cards.

There is another kind of card used for upgrading or evolving your Valkyrie cards.

These are Arcanas' used for upgrading and evolving. On those four Arcana  cards above  the Arcana Strong defense, Force attack and Training are used for upgrading while Arcana Succession is used for evolving Valkyrie cards. What it does is as what it says on the image. More explanataion on it on Valkyrie: Card 3.

This group has Arcana's Blessing which is used for upgrading. The Arcana Stability, Strong turn over and turn over are used for evolving. Stability as it says there prevents evolusion accident meaning the card evovles to something else usually it evolves to what the Valkyrie is opposite to thrTurn over arcana can help you make that happen. Letting the card had an evolution accident can make or break them since it will not only change how the card looks but its skill as well.