Tomoyo is Sakura-chan's kawaii best friend...her RICH kawaii best friend, living in a mansion. This is because her mother, Sonomi, is the president of a toy company. This being so, she can afford to make a WIDE variety of battle (and non-battle) costumes for Sakura. She designs them herself, and I gotta say, she's VERY good. True, her costumes may be...a *little* weird at times, but they're designed to make Sakura even more kawaii, at the same time allowing her to move freely, plus it fits the situation^_^
Tomoyo is also ALWAYS there when Sakura catches cards... Well, at least most of the times. And, when Tomoyo is there, expect her to have a handy videocam in her hand. One of her goals in life is to capture Sakura's "beauty, grace, and elegance on film".
Tomoyo isn't at all clueless, unlike Sakura. She notices *things* about people at once, and she conjures up plans (with a matching kawaii "O~HOHOHOOHO!!!") to help them (blush, Li-kun, BLUSH!!!).
Her favorite color is beige, and her favorite food is sushi. Tomoyo likes singing. She has a very beautiful voice! She has got to be the best singers in the Tomoeda Shougakkou choir, therefore earning for herself solo parts in songs, and helping the choir win awards. She was even "attacked" twice by Clow Cards because of her voice. But, she doesn't let her head get big when she gets complimented. She's very humble, and just smiles gently...Heck, she smiles in every event appropriate!
Tomoyo loves Sakura very much. She worries about her when she's in trouble, but at the same time, she has complete confidence in her cousin. (Oh yeah: Sonomi and Nadesico, Sakura's mom, are cousins) Tomoyo trusts that she can accomplish what she set out to do, even when Sakura doesn't trust herself.
But, Tomoyo is not just a girl behind the scenes. When Sakura is in trouble, she tries to think of ways to help her, as well. Tomoyo knows Sakura VERY well. Even when Sakura says she's fine when she's not, Tomoyo is the first to see through it. She's always there for Sakura, helping her out in any way she can --- the best friend in and out of the battlefield.