Yuki Yuna is a Hero Season 1 Episode 8

Blessings of the Gods

After Fu informs the others that their battle isn't over yet, with each girl besides Karin receiving an additional fairy, the girls soon come up against another forestization. Discovering the remaining Vertex, finding it to be overflowing with cores, Yuna quickly disposes of them using the power of her new fairy, causing some worry amongst her friends. When the forest disappears, Yuna and Mimori end up separated from the others, having been summoned by a hospitalized girl, who reveals herself to be a former hero named Sonoko Nogi. Sonoko reveals to them the secret of the Hero System, in which heroes permanently lose the use of a bodily function in exchange for the power granted by the Mankai form, further revealing that heroes are effectively sacrifices to Shinju who can never die. On top of the shock both girls feel upon hearing this, Mimori is also saddened as she seems to know Sonoko, but is unable to remember her.