Yuuri Asuka

Yuuri and Airi, classmates, met when Yuuri tried cooking for their entire class. A student claimed to have gotten food poisoning from Yuuri's cooking, which sent her into such a state of shock that she did not return to school until Airi visited her and helped prove that the student was trying to frame Yuuri. Two years later, Yuuri is attacked by a witch and saved by a magical girl with a black hat and cape. She asks the girl to cure Airi, but she advises Yuuri to make a contract herself. Yuuri visits her sick friend soon after, who has been told she only has three months to live. When she asks Airi if she wants to continue living, Airi says that wants to live longer and eat delicious things with Yuuri. Yuuri then gives her a spoon, which she calls a good luck charm. She then leaves to secretly contract with Kyubey so she can wish for Yuuri to be cured - it's implied Kyubey had been in contact with her prior to this, probably due to her having been saved by another magical girl. She next see Airi when she learns that her illness has miraculously healed. Airi claims that the spoon cured her, and Yuuri doesn't try to correct her. Once she became a magical girl, Yuuri fought witches (she is also seen fighting against Kyoko Sakura in a flashback) and also cured the illnesses of other sick people. However, this put a strain on her Soul Gem. Sometime later, Yuuri participates in a cooking contest for a restaurant. Airi gives her back the spoon, asking it to help Yuuri. Airi promises to take Yuuri to Bistro Tachibana if Yuuri wins. Though Yuuri makes it to the final round, she doesn't appear at the stage, prompting Airi to go look for her. Unfortunately Yuuri had transformed into a witch, right in front of them. As a witch, she nearly attacked Airi, but was killed by the Pleiades with a barrage of large arrows (similar to the ones Airi uses later, as Yuuri). When she dies, she drops the spoon that Airi gave back to her. Later, Kyubey informs Airi about what happened to Yuuri, causing her to become a magical girl with Yuuri's appearance. Her sole purpose was to avenge Yuuri. Her weapon is a Giant multi-needled hypodermic needle. Source: Puella Magi Wiki