Girls

Example Card: Sakurai Akane

If you want to see the girls and cards list, you can visit http://gamedb.xii.jp/gf_kari/

The page use Japanese but I think its easy to figure it out... hope that helps you, now for the explanation:

This game consists of large amount of girls. Each girl can have multiple set of cards. Please note that you can only fuse card in the same set.

Each card has their own stats which consist of

1. Rarity - (レアリティ)

Each card has a rarity level: N (ノーマル), HN (ハイノーマル), R (レア), HR (ハイレア), SR (Ｓレア), SSR, UR
You will get alot of low rarity cards by going to school, cupid, or events.
High rarity cards are obtained by various way such as gambling real cash for a chance at it, or by completing events.

2. Level

Each card have a fixed max level. You can see it in the roster menu. The only way to level up the card is by yell. If you maxed out the card's level before fusing/merging it, the merged card will receive 10% of the stat from the card that is maxed.  

3. Progression Stage

As mentioned above, each girl is represented by a few "sets" of cards. Each set of card has one card for each progression stage. If the max progression stage is three, it means there are 3 card in each "set". You can see the progression state by the number of ☆ on the bottom right of the card. 

4. Favourability - (好感度)

Each card have a favourability rating towards you. Going to school may increase favourability of a random girl that you have set in the main team or as your favourite girl in the card deck menu. Maximum level for favourability is 5, you can check it by the number of heart shape in the card's profile. When favourability is maxed, card's power will be increased by 10%. However, favourability cannot be raised beyond a certain point if card are not progressed to the final stage. You will also get to enjoy a special chat when the girl's favourability is maxed. (Not much for a chat per se, more like reading the text and hearing the casting voice's lines)

5. Growth - (成長)

Growth on the cards works the same way as experience on your avatar except that growth is obtained by yell. Accumulate the required amount of growth and the card levels up. Each level on the card will have an increasing growth requirement which you can see as orange bar in the card's profile. The card's power cannot be increased further when it has reached the maximum growth.

6. Cost - (コスト)

Each card will have a cost. This value indicates that the card will cost this amount of point to be deployed in the card deck.  Having more Attack Points will mean being able to use cards with higher costs.

7. Attack Power - (攻)

Each card has an Attack Power value used to "damage" opponents in battles against other players or enemies in events.  The higher the Attack Power, the more "damage" you will do.  Cheers by R girls or higher may boost the Attack Power of a friendly card of the same type or all cards or lower the Attack Power of an enemy card while you defend.  If your Attack Power is higher than your opponent's Defense Power, you win the battle.

8. Defense Power - (守)

Each card's Defense Power value is used when you are being attacked by another player during a battle.  The Higher the Defense Power, the more "damage" you will defend against.  Again, R girls and higher may have a special cheer that will reduce damage taken.  If your Defense Power is higher than your opponent's Attack Power, you win the battle.

9. Cheer (声援)

Girls with a rarity of R and above have also a cheer skill.