A Fearless Friend

"A Fearless Friend" (Japanese: 君のためにできること) is the twenty-fifth episode in season three, and the seventy-seventh overall episode of Sonic X.

Plot
When the giant seed finally reaches the final stage of its metamorphosis and starts sucking the life out of everyone except for Cosmo, she takes the Chaos Emeralds to Dr. Eggman, thinking that he'll know what to do. Dark Oak attacks Cosmo, who drops the Chaos Emeralds into space. Thankfully, the Planet Egg responds to the Chaos Emeralds and the Chaos Emeralds' power is restored again. Sonic and Shadow, who use them to transform into Super Sonic and Super Shadow, attack the Metarex seed. Cosmo feels helpless but her mother, in her mind, assures her that she is the one who will save the galaxy. She then transforms into a new form and becomes determined to stop this once and for all. She flies over to the planet, passes through the gravitational force that neither Super Sonic nor Super Shadow could pass through, and plants herself on top of it. She then becomes a tree, saying that she has now immobilized Dark Oak. She tells Tails to load and fire the Sonic Power Cannon and shoot it at the planet. Everyone is shocked and does not know whether or not to risk saving the galaxy if they're going to kill Cosmo in the process. However, Tails is very hesitant, but Cosmo re-assures him that her seeds will be spread throughout the galaxy (American and European dubs only). He then thinks back to all of the good times they've had and their love and, tearfully, admits that he loves her (Japanese/French dub only), and fires the Super hedgehogs at the planet, completely destroying it, including Cosmo. In a white void, Cosmo thanks Tails about what he done for all of the good times and Cosmo said "I love you Tails" before she disappears (Japanese/French dub only).