Info on Cosmo from Sonic X:
Cosmo wasn't born yet when her entire race was pratically wiped out by the person who supposedly is her father. Her fathers real name is Lucas but when he does what he did, his name was Dark Oak. When they attacked the station that Cosmo and her family was in Cosmo was captured and eveyrone else she knew and loved was killed.
Cosmos race was called the Seedrians. The males didn't look like plants they looked like Ferrets, while the females were plants. Cosmo and her sister Galaxnia and everyone else was born from this tree that used to be a Seedrian called Earthia. Cosmo essentially besides the five leaders of the Metarex are the last of the Seedrians. She fell to Mobius, Sonics home planet where she was found by the hedgehog Amy, the rabbit Cream and the Kitsune fox Tails. Shortly after she arrived there one of the Metarex generals attacked and took the life force of the planet. So they have to head into space. Those that are going are, Sonic, Tails, Cosmo, Amy, Cream, Creams pet Cheese, Chris (a friend of theirs from earth.), and Knuckles. But they didn't know is that Eggman (or Robotnik), is following them to get the Chaos Emeralds back also because Sonic had to cast them away so Dark Oak wouldn't get them. Season three is opened up with Sonic fighting Dark Oak outside Mobius. And Sonic can't win. Even though he is Super Sonic.
They go through tons of adventures one of which is my favorite where they are stuck on a forest planet and Cream, Cheese, Amy and Cosmo go out looking for Sonic and they cme upon a metarex with the life force of htat planet. And they fight him several times and he keeps losing easily to them. (And they say women can't fight in anime.) They eventually come across Cosmos home world. And find out why she grew up on a colony. During all this stuff thats happening Tails and Cosmo get close. As the final battle is drawing near they find out why the Metarex can find them so easily. Cosmo has a tracking device inserted into her eye and her brain. And they reveal that if they remove it that if she doesn't die, she would never see or hear again. So she tries to get off the ship, but Tails stops her. And I swear if noone walked in on them, those two would have kissed.
As sometime in season 3, they find out that Shadow is still alive and he starts hunting Cosmo down because shes a threat to everyone because of that tracking device. But Tails won't let him near her. Eggman also has struck a deal with Dark Oak, which screws him over in the end and he allies himself with Sonic for the final battle. But during the final battle it turns out that Dark Oak has all seven Chaos Emeralds. And is planning on using them with the life force of every planet he has come across and kill all life on each one. The only one who isn't phased by whats going on is Cosmo. So she stops whats going on (I Don't remember how). But she loses the Chaos Emeralds but somehow they turn Sonic and Shadow into Super Sonic and Super Shadow. Which beats Dark Oak for now. Until he squeezes the planet he made into a core explosion to destroy the entire galaxy.
But right before it happens Cosmo gets a message from her mother, Earthia. Telling her shes the only one who can stop Dark Oak. So she flies out to the planet and stops him from blowing it up, but it turns out the only way for them to stop Dark Oak now, is for them to fire the Power Cannon meant to fire Sonic out of at the planet and destroy it. Tails is the only one for some reason who can do it. In the English version Tails didn't want to shoot Cosmo because she was his friend, and Cosmo felt the same way saying she would never forget him. But in the Japanese version, Tails refused to do it because he loved her. They have a scene between Tails and Cosmos spirit after Tails shoots the cannon, saying that they will never forget each other and right as they are ending the episode Cosmo tells Tails she will love him forever. The last episode of the series is both hard to watch in both English and Japanese. The only thing they ever found of Cosmo was a seed, its sad to say but you can see exactly the moment Tails heart shatters. As soon as he see what Sonic givese him his heart shatters. He crying because he lost his friend in the English version. In the Japanese version its because he had to kill the love of his life. And that he believed in Sonic and that Sonic failed him in not saving Cosmo.
One thing they did right in the last episode in English was they had a scene with Cosmo telling everyone she was happy. And for Tails to not be sad. They also had a scene with Sonic having a conversation with Cosmo, telling him to tell Tails that she will always be there for him. Japan in my eyes did that episode badly. They didn't have that scene in it at all. At the end of the episode as everyone is getting ready to stop Eggmans next plan they show a plantpot with a rose growing inside of it, there has been speculation when that thing grows it will become Cosmo. But I don't think it is true, because I think Cosmo is still alive. And they proved that in the last episode because her voice was coming from a tree next to Sonic.
As for cosmos appearance, she has a green hair and where ears usuallly are she has rose buds. She has a dress that resembles a flower also, sometimes I wonder if that is part of their body already. Her dress is a green/white color.
This is the end of my explanation of Cosmos past and stuff. I know this isn't very good, but I have only watched a few episodes in Japan of season 3 and only watched it once in English.