fuu's magic, as you must know by now, involves wind and is associated with the earth. she has the most spells of the three magic knights and the most variety of spells. hikaru's fire magic is offence. umi's water magic provides defense. fuu's magic involves both of these and she also has a healing spell.
winds of healing: the first spell that fuu learns, in episode four/the second manga after umi defeated alcyone and was badly wounded. unlike hikaru and umi, she didn't need to learn her magic. as clef told her, her magic was awakened by her compassion and desire to help umi.
green gale: fuu's second spell, offence. simply a gust of wind directed at the target, blowing them away.
winds of admonishment/binding winds: somewhat of a combination of offence and defense. swirls of wind surround and trap the target, keeping them from charging or running off.
winds of protection: this spell was learned on a spur-of-the-moment, in the sea shrine while fighting against ascot's monster. this spell surrounds the target with a barrier, protecting it from attack. of course, if an opponent is powerful enough, it may break through the barrier.
green tornado: from season two, this attack is much like the spell green gale only much more powerful.
all three of the knights have armor, which has the same basic design: cape, headpiece, gloves (one with a gem on it), boots, another jewel just below the collar, and shoulderpads. but each of them is slightly personalized.
fuu's is, of course, green. her headpiece is a green headband with two wings adorning it that are so cute. her gloves are elbow-length and her shoulderpads resemble those of windam's, her mashin: gold with those... cool-looking hanging-down things. ^.~; as usual, her footwear is the shortest of the three (hikaru's are always knee-length and umi's go most of the way up her leg).
it sounds strange to have noticed, but bear with me here. i've observed that as a magic knight in her full armor, fuu's figure (specifically her chest) is more developed. fuu's chest is usually very tiny, but as a knight, she's much fuller (of course it depends, too, on the artist ^^;). i believe this was done intentionally. the filling of her figure as a knight kind of symbolizes how her heart has matured by showing a more matured body. as a kinght, she is not a young girl, but a mature woman, and her figure demonstrates this. or maybe i just read into these things way too much.