Cosmo

ails" Prower, Cream, and Amy were the first to find her, and they questioned her arrival. Cosmo told them that she was looking for the "legendary hero that can use the Chaos Emeralds, Sonic the Hedgehog." However, she refused to tell them any more. Later, while in Tails' ship, she spotted Sonic and hopped out to greet him. Cosmo pleaded for Sonic to help her.

Sonic agreed to help her and he, Cosmo, Tails, Knuckles, Amy, Cream, Cheese and Chris Thorndyke, who recently arrived on Sonic's world, began travelling through the universe in Tails' new space ship, the Blue Typhoon in search of the Chaos Emeralds which Sonic scattered through the universe during his first battle with Dark Oak.

Later in the series, Shadow boarded their ship and attempted to kill Cosmo, as he believed her to be a spy for the Metarex, but Cosmo's friends managed to keep her safe. Tails especially endeavored to keep her safe, to the point of almost being knocked unconscious. Before Shadow could do Cosmo any harm, a Metarex broke in and stole the Chaos Emeralds. The Metarex called Cosmo "White Seed" and told her that she did a good job. Cosmo then remembered that before she escaped from her space colony, the Metarex were planning to use her as a spy.

Knuckles and Tails managed to locate an invisible signal and found that it was attached to her brain; if they had gotten rid of it, Cosmo's hearing and sight may have been lost in the process. Knuckles said that it would have been best to do that, but Tails refused to harm Cosmo.

Later, Cosmo learned that she could hear the Metarex in her head and fell into deeper despair. While she was in sorrow, Chris told Sonic that he now understood why Cosmo was able to understand the Metarex language.

In Episode 74, Cosmo ran away but was stopped by Tails. Their friends then showed up and said they were determined to defeat Dark Oak instead of risking Cosmo's hearing and sight. In Episode 77, Cosmo sacrificed herself by fusing herself with the Dark Oak planet to make it weaker so that Tails, Super Sonic and Super Shadow could destroy it and save the universe. At first, Tails refused to, but Cosmo convinced him that it was the only way to save the galaxy. Tails trusted Cosmo and ended up shooting her (in the Japanese dub, he yelled that he loved her while doing so) with the Sonic Driver (Sonic Power Cannon in the English dub), causing her to be killed in the process. In an attempt to rescue Cosmo from death, Super Sonic and Super Shadow used Chaos Regeneration, but all they managed to produce was a small seed. In episode 78, when Sonic arrived back on board the Blue Typhoon, he handed this seed to Tails, who collapsed with grief as he realized that Sonic was unable to save Cosmo. However, the seed sprouted in the end.

Personality
Cosmo is a kind and gentle character, though she often feels guilt because she was unable to save anyone from her home planet. She also seems to suffer from a low self-esteem issue, often calling herself "unworthy" or blaming herself for the hardships that she and her friends had to endure. Cosmo also dislikes violence, but acknowledges that fighting is sometimes a necessity, although she herself is unable to fight. Cosmo can be somewhat clumsy, but she is also quite resourceful; she also has a penchant of getting into trouble.

Cosmo shares similar qualities with both Maria Robotnik and Tikal the Echidna. Both Maria and Tikal sacrificed themselves to save their friends/beliefs and are pacifists, but know how to fight when necessary.

Abilities and weaknesses
Cosmo does have a few abilities, being a plant herself, such as having the ability to empathize with plants, trees, or the planet and determine their state of life. Cosmo can jump high and gently float down with the aid of her skirt. She also appears to be able to unlock the power of a Planet Egg, as demonstrated in episode 58, where She caused the planet egg to activate and grow vines that entangled Dr. Eggman's machines, but also her friends and herself due to her lack of control over the vines. When Cosmo is in her adult form, she is able to turn into a tree and weaken other planets.

Cosmo's weaknesses include being physically weak and acting a little clumsy. She has trouble carrying heavy objects but can use certain objects as defense. She also shows heavy endurance as she is able to recover from powerful attacks quickly as seen in episode 58 where she quickly arrived back to attack a metarex with fruits after being sent flying into the air by a heavy branch shaped like a club. Cosmo also tends to get into trouble easily. She also might have air sickness as when Tails was flying high above Angel Island, she was shown to be very dizzy and when Amy was trying to catch up to Sonic, she sped up her ship but Cosmo wasn't feeling well so Amy held back.

Family
The only confirmed members of Cosmo's family is her mother Hertia (Earthia in the English dub), who is the leader of the Green Planet council, and her older sister, Galaxina, who worries about Cosmo and her mother.

Earthia/Hertia: Her mother, who is the leader of the Green Planet council. She decides to leave the planet when it becomes too dangerous, but is later killed after the Metarex board her refugee ship. In the dub version of Sonic X, she is instead known as Earthia. During Episode 78, she appears to Dark Oak--now returned to his form as Lucas--and speaks with him, telling him that thanks to Cosmo they now have 'another chance' together; however this dialogue appears only in the dubbed version. This has brought about suspicion that they were previously in love. It also brings the possibility that Cosmo's race will regenerate, though this is unlikely.

Galaxina: Her older sister, whom is shown to worry a great deal about Cosmo and their mother, Hertia. She is portrayed as very smart, sophisticated, and down-to-earth, the opposite of the dreamy Cosmo. She appears to perhaps be the eldest--or most authoritative--of the family who are shown in the beginning of Episode 77, while Cosmo is an 'infant'. She seems to look more like Hertia than the others. She also is one of the few to have a daisy on top of her head rather than two rose buds on the sides of her head. In the original Japanese version, she and the others on the ship had no official names in the show. In the original Japanese version, Galaxina has no name; she was referred to as one-sama ("big sister") by other members of her clan.

Seedling: Possibly Cosmo's child, a seed that was given to Tails by Sonic in episode 78, after Cosmo's death. It is yet unknown the name of this seed, or if it will survive. It could possibly be Cosmo herself, seeing as the seed it grew from is a white one, just as Cosmo had the Metarex codename, "White seed". Several fans venture to believe this to be a means of revival on her part. Alternatively, it could also simply be a part of Cosmo - all that Sonic could obtain. Plus, it could grow into just a regular plant (rather than a sentient one) as it is seen in the finale, and in Sonic Chronicles The Dark Brotherhood growing in a flower pot in Tails' workshop where it is much taller in size, however, there is no reference in this game, so it is unknown if it is her. In the Japanese version, Sonic and Shadow use Chaos Regeneration, which could also lead to the fact that the seed is most likely Cosmo over a Seedling.

Cosmo is also friends with the crew of the Blue Typhoon.

Romance
Cosmo became good friends with Sonic and friends, but most particularly with Tails. The two of them ended up alone on a mission together at one point. Tails later protected Cosmo when Shadow targeted her for assassination. Tails continued trying to stop Shadow even when he was very badly injured by him. In the Japanese version of episode 77, Tails screamed I love you, Cosmo!, just before he fired the Sonic Driver towards her and Dark Oak.

Also, when the team went to an alien planet, Amy bought a potion that when two people fall into a pool of potion (that had been poured into the pond), they would fall in love, but instead of Sonic and Amy, Tails and Cosmo accidentally fell into Amy's trap for Sonic and fell into the pool on the full moon which activated the potion. (In case they forgot, one of the aliens said that it was so powerful, that the two will always be together.)

While some characters are having their fortune told (Planet of Misfortune) Cream inquires about Cosmo's future and the fortune teller states that there is romance in her future, he also says it is strange since 'Plants and animals do not usually get along.' Future events show that this was referencing Tails and Cosmo.

Friends/Allies

 * Miles "Tails" Prower (Love interest)
 * Sonic the Hedgehog
 * Amy Rose (True Friend)
 * Knuckles the Echidna
 * Cream the Rabbit (True Friend)
 * Espio the Chameleon
 * Charmy Bee
 * Vector the Crocodile
 * Vanilla the Rabbit
 * Christopher Thorndyke
 * Shadow the Hedgehog (Ally against the Metarex)
 * Rouge the Bat
 * Dr. Eggman (Ally against the Metarex)

Rivals/Foes

 * Metarex
 * Dr. Eggman
 * Shadow

Trivia

 * In the english dub, Shadow believed that Cosmo was a traitor, despite being the very person who called the Sonic Co. to this mission. However, this is most likely the only reason 4Kids could find to cover up Shadows violent actions in the Japanese Dub.
 * In Sonic Chronicles, Tails' workshop contains a pot plant very similar to the one shown at the end of Sonic X, likely as a reference to Cosmo.
 * Cosmo is also one of the few characters that do not wear gloves.
 * Because it was never actually shown that Cosmo's sisters were dying, it could be possible that they had survived and managed to get aboard the escape pods like Cosmo did, though it is somewhat controversial.
 * As shown in Episode 59 of Sonic X when Charmy appeared dressed up in what looked like trash, everyone attacked him mistaking him for a Meterax as well as Cosmo. Some highly doubt that Cosmo would attack a Meterax head on like that and just think she was made to do that because of the episode's plot, some think she just attacked him because of Charmy's size, although it was probably just for humor.
 * Many fans of Tails and Cosmo think that the Japanese ending to Sonic X was a lot better than the 4kids production during Cosmo's sacrifice, most likely because Tails confessed his love for Cosmo.
 * Though Cosmo has not appeared as a major character in the Sonic X comics, she has gotten two cameos - in the fifth issue, when Chuck Thorndyke talks about possibilities of extraterrestrial life, and in the twenty-first issue, where a toy in her likeness can be seen at the top of the cover.
 * Cosmo is also similar to Lumina Flowlight, and Void.
 * Cosmo bears a strong resemblance to Kirlia from the Pokémon series.
 * While Cosmo's name could be derived from a plant, it is more considered originating from space (Cosmos, Galaxy, etc).