Cosmo the Seedarian

Tails' girlfriend on sonic X. they start to develop feelings toward each other during the course of season 3. She comes to warn Sonic & friends about the metarex, a group of alien robots that steal planet life. In the end she transforms herself into a tree and envelops herself around the metarex planet to immobilize and stop them from destroying the galaxy. This gave tails the opportunity to destroy the metarex for good with his sonic cannon but at a price: cosmo's life. The fact that Tails had to kill the one he loved makes many fans consider it the saddest anime moment in history.