Puella Magi Madoka Magica (2011)

S1E12 My Very Best Friend

Homura faces Walpurgisnacht by herself and suffers grave injuries. No matter how many times she repeats the fight, she simply cannot win, and despair closes in around her. Worse still, she realizes her efforts are only causing Madoka more pain. Overcome by hopelessness, she sinks into deep despondency—and her Soul Gem starts to darken.