D.Gray-Man 1

D. Gray-man is one of my favorite manga series, so of course it's required reading in any language I study! This series follows Allen Walker, a 15-year-old who, as of volume 1, is traveling to become an exorcist, someone who can use special weapons to destroy living weapons called "akuma". Along the way, he meets others who's lives are affected by the akuma, and we learn how the akuma are created (spoiler for midway through volume 1: by taking the soul of a dead person and using it to power a machine that wears human skin to blend in) and who their creator and master is.

I have a difficult time judging what stage of learner someone should be to read something in Spanish; from my own experiences, as of the time of writing I'm someone who took Spanish in school for many years, dropped it for many years, then felt like I shouldn't let it all crumble away. So an intermediate learner shouldn't have much difficulty with this book, at least.