9x12 - Fairy Tail

In X686, Mavis learns the unperfected black magic spell Law from Zeref, which she later uses to save her friends' lives at the cost of her physical growth. She re-encounters Zeref ten years later after she and the rest of Fairy Tail have participated in a four-year-long war. Zeref discovers that she has been inflicted with Ankhselam's curse for using Law, reasoning that Mavis's tactical command during the war has offset her life-stealing powers by dulling her respect for life. Mavis denies Zeref's statements out of disgust, only to later realize the truth when she unintentionally kills Makarov's mother on the day of his birth, causing Mavis to exile herself from the guild. When Zeref finds Mavis again one year later, she empathizes with his cursed state and proposes that they lift their shared curse together. The two fall in love and kiss, but as a result, Zeref's curse kills Mavis despite her immortality.