Spoiler Warning: Spoiler details may follow
As Homura Akemi fought desperately, alone against Walpurgisnacht, her magic powers depleted haflway during the battle, which resulted in her defeat.
As she tried to turn back time, she was reminded by the fact that doing so she will only end up adding a heavier karma on Madoka Kaname. From there, she hesistated.
From the despair she slowly realized from there slowly filled her Soul Gem with despair, polluting it...and when all things looking grim, her hand is reached by a warmth that she felt familar...
Madoka Kaname came to her side, while declaring to Homura that she will be offering herself to become a Puella Magi, seemly disobeying Homura's wish. However, for Madoka, who is filled with confidence on her face, wished to Kyuubey :
「I wished for every witch that exists from any universe to be erased from existence」
Madoka thus transformed into a Puella Magi, blazed through each and every corner of the space and universe, and saved all the Puella Magi that were under the transistion of becoming a witch, and thus prevented them from turning into a witch. With her actions, she has turned into a Goddess that defies the law and the logic of the universe.
Homura, who witnessed all the progress, broke into tears, considering that Madoka's wish will cause her to be erased from existence in any universe. However, Madoka appeared and consoled Homura, telling her that she has seen through everything, and anything that happened to Homura all these while, how hard she worked herself to protect Madoka, and thus gave Homura an encouragement :
「You are my best friend」
Upon the end of the conversation, she passed on her ribbons to Homura, and disappeared.
From there on, a new universe is formed. While everyone there seems to forget about Madoka, only Homura does not. While wearing the ribbon Madoka passed on to her, and from there on, she keeps fighting on as a Puella Magi, with now her new opponent, the Magical Beast, lurks from the shadows...
For a show which was considered by the fans to be full of despair and grim dark elements, the episode itself surprisingly brought many emotional reactions to the fans : From crying, to heavy sighs (sigh of relief or sigh of bittersweetness). It is also considered to be a countertag and the opposite to Desperation even with struggling and Chidamari Sketch tags.
This tag is especially tagged with illustrations that depicts Ribbon Homura with Goddess Madoka, while other variants exist.
Puella Magi Madoka Magica
You are my worst friend - a countertag to "You are my best friend", hillarity ensures and also a mood breaker to otherwise a very touching scene.