Garo: Vanishing Line

The anime's story is set in a prosperous city named Russell City. Even as the city celebrates its success, a conspiracy that threatens to shake its world has been set in motion. A man named Sword is the first to hear the earliest stirrings of the plot, and throws himself into a shadow war in order to expose it. His only clue is the keyword "El Dorado." He meets Sophie, a woman searching for her older brother who left her with only a message with the same word: "El Dorado." With Sword having also lost his younger sister in the past, both are drawn together by the word, and work together to find out its meaning.

(Source: Anime News Network)