Triple Triad

In addition to the Final Fantasy VIII game itself, there is a sort of game-within-a-game: the card game Triple Triad is all the rage in Garden and the Final Fantasy VIII world. Quistis is Balamb's resident Triple Triad champion, and she, as well as all the other characters in the game, has a character card. In order to gain this card, you need to defeat any of the Trepies (the guy in the cafeteria or the two girls in the 2F classroom). Any character card is rare and very strong, so the Quistis card is hard to gain and will be a great addition to your card stash. One Quistis card will refine 3 Samantha Souls.

There is also a CC group sidequest in the game; by finding and defeating all seven members, you can collect rare and powerful cards to add to your collection. In order to face the entire group, you have to challenge them individually from lowest-ranking to highest-ranking.

Jack
Location: Balamb Garden Hallway near the Directory. He often enters from the bottom of the screen on either side of the hallway.
Rare Cards: none

Club
Location: Balamb Garden Hallway near the Cafeteria. He appears randomly and so is hard to find.
Rare Cards: none

Diamond
Location: Balamb Garden Hallway in front of the Directory. Diamond is actually two female cadets instead of one whole person.
Rare Cards: none

Spade
Location: Second Floor next to the elevator. He is one of the two people you often seen around there.
Rare Cards: none

Heart
Location: Bridge. Heart is none other than Xu!
Rare Cards: Carbuncle

Joker
Location: Inside the Training Center. He appears randomly and isn't always there, so he's a bit hard to find. Once you beat him, he will also upgrade your battle metter to include GF information. If you have defeated Jack, you can challenge Joker any time afterwards.
Rare Cards: Leviathan

King
Location: It's actually Quistis, but you have to do a sequence of events before she reveals herself. Speak to Nida on the bridge, visit Dr. Kadowaki in the Infirmary and challenge her to a game. In the process, she will reveal that she was once Card King but lost the title four years ago; return to Squall's room and take a nap. Lo and behold, the King will arrive!
Rare Cards: Gilgamesh

Return: Quistis