Earth: Yosou's naturally in Earth element. (happy, relieved whatever) He can heal and make plants grow... and a few other bits and pieces. Generally nothing very offensive beyond making the enemy trip over roots.
Water: This is when Yosou get *depressed*. His eyes go blue along with his robes/gi and those little green leaves turn into water dropets. He can jet people with water and do various things with the direction and purity of water, make it rain etc. That is, if you can get him to feel like doing it... When in water form, Yosou constantly has a small raincloud over his head.
Air: This is when Yosou get scared (fear, shock etc). His eyes go a light grey colour, and his hair tints grey. He also get wings. (Slightly more chicken-like wings than some, but still, wings) These are very, very useful. Especially considering he often goes into air mode whilst half way down a cliff. He can use some pretty good wind attacks from small cyclones and storms to those cute little willy-willies which stir up the leaves a bit. Yosou has had a lot of practice with air because of the large amount of time he spends falling down cliffs or simular situations. Yosou is pretty much a coward, or just plain unlucky.
Fire: It's pretty rare that Yosou goes into fire mode, which is when he gets angry. He doesn't get angry very often, mainly because getting angry requires a little bit of courage. Yosou's more the kind of person to go "AaaaaaaAAAH! You hurt my friends! ...*that means (insert enemy here) can hurt me too* RUN FOR IT!!!" and hide under the nearest couch. The only other times he been into fire mode is when he's been teased/annoyed by Lisa-The-Anime-Goddess. Or Risa saying something particularly stupid. When angry, his eyes go red and his hair gets tinted red. When in fire mode, he can incinerate things and a few other spells, but generally, the first one is enough.
Lightning: This is when Yosou gets Really really really pissed off. Very rare. (He can also get like this from the extremes of the other elements) Eyes go gold, same with robes and lightning symbol. Can zap people. Very ouchies. (Lightning's Yosou's *ultimate form*. He's only gone that far once before, and is only generally much use when he's in it. Lightning is VERY STRONG)
Yosou get's neurotic over people calling him anything even vaguely to do with Chickens, Chocobos etc. He usually ends up screaming "I AM NOT A CHICKEN/CHOCOBO/CHIKOBO/CHOKOBIN!!!!!!!!!!!"