While supporting the artist by purchasing the books is always recommended, there are legitimate legal avenues to read the series for free or included with subscriptions.
Zombillenium, Vols. 1-2: Gretchen/Human Resources - Amazon.com zombillenium english free
13 (Season 1)
If you have a library card, search these apps to borrow the graphic novels digitally for free. While supporting the artist by purchasing the books
If you have ever felt like your job is sucking the life out of you, Zombillenium might be the most relatable animated series you’ve never seen. zombillenium english free