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This character exists primarily or exclusively within the Sonic X continuity.
Information in this article may not be canonical to the storyline of the games or any other Sonic continuity.
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Thank you all for your friendship. Before I met you, I didn't believe in myself. My clan was wiped out by the Metarex. I felt like I was helpless and couldn't do anything to stop them. But because of you, I learned that I didn't have to stand by and watch the Metarex take over. I could do my part to fight back and help restore my clan. I just wanted you to know that I'm happy now because I fulfilled my destiny. Remember, I'll always be with you.

— Cosmo, "So Long Sonic"

Cosmo (コスモ Kosumo?) is a main character from the anime series Sonic X. She was a female child of a plant-like alien species whose home world was destroyed by the villainous Metarex, who, in the years that followed, left Cosmo as the sole survivor of her kind. To thwart the Metarex's ambitions for universal dominance, Cosmo joined Sonic the Hedgehog and his allies in their war against the Metarex, eventually becoming a love interest for Miles "Tails" Prower, but she sacrificed her life to defeat the Metarex for good.


Cosmo is a short, humanoid plant with pale peach skin, and light blue eyes with one long eyelash on each one. She possesses short bright green hair with a pair of paradise pink flower buds held it by golden hair ties, one on each side of her head. She wears a green and white dress with long sleeves, gold cuffs on the end, and gold trimming, a red amulet, white leggings, and green slippers.




Cosmo's former home world was destroyed by the Metarex before she was born, and she was instead raised on a space colony. She lived peacefully there until the Metarex came and began to destroy her new home, including her family (which included Earthia). As Cosmo was escaping, the Metarex planted a tracking device on her. Cosmo also had a device inside her brain, which when activated, allowed the Metarex to hear and see everything that she did, allowing them to always be one step ahead of their enemies.

Metarex Saga

Cosmo crash lands on Sonic's planet.

After the attack, Cosmo escaped into a ship and arrived on Sonic's planet. Tails, Cream, Cheese and Amy were the first to find her and they, except for Cheese, questioned her arrival. Cosmo told them that she was looking for the "legendary hero that can use the Chaos Emeralds, Sonic the Hedgehog." She refused to tell them any more. Later, while in Tails' jet, the X-Tornado, 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 Christopher Thorndyke, who recently arrived on Sonic's world, began traveling 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, leader of the Metarex.

Later in the series, Shadow raided the Blue Typhoon 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, especially Tails, who 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 interrupted the fighting. Dark Oak called Cosmo "White Seed" and praised her for completing her mission. Cosmo then remembered that before she escaped from her space colony, the Metarex were planning to use her as a spy.

Chris and Tails managed to locate an invisible signal and found that it was attached to her brain; if they removed it, Cosmo's hearing and sight may have been lost in the process, rendering her deaf and blind, possibly permanently. In the English version, Knuckles said that it would have been best to do that, but Tails refused to harm Cosmo. In the Japanese version, however, Knuckles yelled at Tails that there had to be a way to remove it without hurting Cosmo, to which Tails yelled back that he had no idea how to do both, assuming it was possible.

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

Cosmo's seed.

In episode 74, Cosmo tried to run 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 and restore her clan. At first, Tails refused to pull the trigger knowing it would mean Cosmo's death, but Cosmo convinced him that it was the only way to save the galaxy. Tails trusted Cosmo and ended up shooting her (while yelling that he loved her while doing so in the Japanese version) with the Sonic Power Cannon, causing her to be killed in the process (in the ending credits, she says to Tails that she loves him, while in the dub she says she'll never forget him). When Cosmo's spirit sees Tails she kisses him on the lips. According to the Japanese version, 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. (However, in the English version, Chaos Regeneration is not used and Cosmo implies that the seed is her child.) In So Long Sonic, when Sonic arrived back on board the Blue Typhoon, he hands the seed to Tails, who breaks down in tears.

In the very end of the series, the seed, which Tails has planted in a pot at his workshop, begins to sprout.


Cosmo is a kind and gentle alien, although she often feels guilt, anger, and overwhelming sadness due to being unable to save the rest of her species from destruction at the hands of the Metarex. She also seems to suffer from low self-esteem, often calling herself "unworthy" or blaming herself for the hardships that she and her friends had to endure. Cosmo can be somewhat clumsy, but she is also quite resourceful. She will often rush headfirst into danger with little sense of self-preservation, even into situations that she knows to be a trap, which can be put down to her survivor's guilt spurring her to sacrifice anything to atone for saving herself while her family perished at Dark Oak's hands. Cosmo strongly dislikes violence and the need for conflict in life, like her father Lucas in many ways, but unlike him acknowledges that fighting is sometimes a necessity and that struggle and conflict are a necessary evil to achieving a better future.

Powers and abilities

Cosmo does have a few abilities, such as being able to empathize and communicate with plants, trees, or the planet itself and determine their state of life. Cosmo can jump very high and use her skirt like a parachute to gently float down. 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. At the end of episode 73, Cosmo's amulet begins to glow before she teleports the Blue Typhoon away from Dark Oak and back to her homeplanet Green Gate, though this ability is never explained afterwards and caused her to faint from the strain.

In episode 59, Cosmo has demonstrated some sort of agility as shown when the Chaotix were about to leave and kidnap Cream with a sack, she quickly rolled next to Cream letting herself get captured along with Cream and later on when Vector and Cosmo get into a fight, she is able to avoid his attacks with speed and thus gained the upperhand. 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. She is able to read and decipher the Metarex language, either due to the implant in her brain or their shared origins on Green Gate.


When Cosmo removes her amulet she can enter a transformed state, wherein she is able to turn into a tree and bond herself to Final Mova's third phase. Presumably she is able to bond to machinery in this form as Earthia did with their ship's navigational system, and in the dubbed version it is heavily implied to be the form her species must take to birth children. Eggman describes this state as what happens when a member of Cosmo's species reaches maturity, though it causes them to "wither and perish" immediately afterwards if they are not sustained by artificial Planet Egg energy as her mother was on their ship.


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. Cosmo also tends to get into trouble easily. She also might have air sickness as in episode 53, when Tails was flying high above Angel Island, she was shown to be very dizzy and in episode 63, when Amy was trying to catch up to Sonic, she sped up her ship but Cosmo wasn't feeling well so Amy held back.



Earthia is Cosmo's mother who is the leader of the Green Gate council. She decides to leave the planet when it becomes too dangerous, but she is later killed after the Metarex board her refugee ship. 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. Though originally incensed by Earthia's murder at her father's hands, Cosmo comes to see her mother in a much less innocent light after learning that it was her spiteful actions on Green Gate that created the Metarex, although this aspect of their relationship appears only in the Japanese version.


Cosmo and Galaxina.

Galaxina is Cosmo's older sister who worries a great deal about Cosmo and Earthia. She is very smart, sophisticated and down-to-earth, the opposite of the dreamy Cosmo who 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'.

Dark Oak

Dark Oak is the father of Cosmo and the husband of Earthia. She has a strained relationship with him, as Dark Oak would treat her more like a subordinate than a daughter. Due to this, Dark Oak would be willing to fight Cosmo should she get in his way. Cosmo herself despised her father's deeds and turned on him. Nonetheless, on learning of her father's tragic origins Cosmo comes to empathise with Dark Oak somewhat, and recognises him as the last remaining member of her family. In the Japanese version, Cosmo eventually mourns the fact that she and her friends learned to see past their differences yet she cannot do the same for her father - questioning if he genuinely hates animals as much as he claims or if his actions are nothing but revenge against her mother. On attempting to restore the Chaos Emeralds, Cosmo attempts to reason with Dark Oak, debating her hope that their species can coexist with animals one day against his jaded cynicism that her dream is impossible to achieve.

Miles "Tails" Prower

Tails and Cosmo watching the moon.

Don't be sad, Tails. Whenever you miss me, just look for me right here beside you.

— Cosmo, "So Long Sonic"

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 when Tails got hurt, Cosmo stitched his bruise and Tails blushes in return. Later on, when the Blue Typhoon meets the Chaotix for the second time; in return for Tails repairing the Chaotix's space ship, the Chaotix noticed that Tails is starting to have an affection for Cosmo so the trio tried plans to join the two together in love. Although those plans failed, Tails and Cosmo's relationship seemed to be more intimate, even to the point of Tails saying "Cosmo, you're so beautiful" but didn't have the courage to completely say it and Cosmo misheard it, thinking about something else.

Their love for each other is confirmed in the episode "The Planet of Misfortune" when the Blue Typhoon lands at Planet Marmolim. There, 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," which foreshadows future events throughout the series between Cosmo and Tails. Although Amy has set-up a trap to lure Sonic into the lake, Tails and Cosmo accidentally trigger it themselves, leaving the duo in love for each other while watching the moon, much to Amy's disgrace.

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 episode 77, Cosmo plants herself on Dark Oak (in her metamorphosis form) to immobilize him, telling the heroes to fire the Sonic Driver/Power Cannon at Dark Oak, however, this would also kill her, much to everyone's dismay, especially Tails'. In the Japanese version, when it's up to him to fire the Cannon, Tails was extremely hesitant to do so and had a brief emotional breakdown, but with the help of Eggman's reassurance, Tails screams his love for Cosmo just before he fired the Sonic Driver. In the English dub, he never directly stated such words; it is strongly implied that Tails simply did not have the courage, even at the end, to admit that he loved her. When Cosmo's spirit visits Tails she kisses him on the lips. In response, Cosmo says in the Japanese version that she will always love Tails before ascending into the afterlife, while in the English dub she said that she will never forget him.

Amy Rose

Amy Rose is one of Cosmo's best friends. At first, Amy despised Cosmo when she announced that she had crossed space to find Sonic and threatened her not to approach him since she claimed to be his official girlfriend. In the end, Amy recognized Cosmo as a tragic victim and agreed to help him rescue the worlds the Metarex has conquered. During the trip, Amy encouraged Cosmo to go through with her choices and fight to achieve her goal. She later mourned her sacrifice against Dark Oak.

Knuckles the Echidna

Cosmo talking with Knuckles, from "An Enemy in Need".

Knuckles and Cosmo are seen having a few interactions. Although Knuckles did not trust her at first, he develops a warm and friendly attitude towards Cosmo later on where they usually get along well, but Cosmo still joins the others in mocking him. However, Knuckles is generally protective towards Cosmo and he cares about her well-being.

Christopher Thorndyke

Cosmo and Chris.

Chris is a friend of Cosmo as well, they get along pretty well. Cosmo starts to look up to Chris after he nearly succeeded in rescuing her from Black Narcissus during which time Chris tells Cosmo that she reminds him a lot of himself before he met Sonic. Like the others, Chris is greatly saddened when Cosmo sacrifices herself to save the Galaxy.





  1. 1.0 1.1 Sonic X episode 65, "Mission: Match Up"
  2. 2.0 2.1 2.2 2.3 Cosmo's eyecatch card
  3. Yoshimura, Kiyoko (12 November 2005). "An Underground Odyssey". Sonic X. Season 3. Episode 62.
  4. Masaki, Hiro (4 February 2006). "Clash in the Cloister". Sonic X. Season 3. Episode 66.