Yuki Yuna is a Hero Season 1 Episode 9

Those Who Know Grief

Yuna and Mimori relay what they've learned from Sonoko to Fu, who asks them not to tell Itsuki and Karin until they know for certain. Despite hearing from Itsuki's homeroom teacher how Itsuki has been suffering due to her missing voice, Fu remains in denial, hoping that things will eventually get better. The next day, however, Mimori reveals to Yuna and Fu that their fairies were actually created to prevent them from dying, even by suicide, proving that everything Sonoko said to them was true and that their symptoms are permanent. This leads Fu to become distressed, knowing that Itsuki's voice will never return and she will never achieve her dream of becoming a singer. Angered by having gotten everyone involved, Fu seeks to destroy the Taisha, even preparing to battle her way through Karin to this end. However, Yuna and Itsuki stop her from fighting, showing her they have no regrets joining the Hero Club.