the monster inside me wasn't inside me

Volume 1 cover Monster is a manga series by Naoki Urasawa, published in Big Comic Original magazine from 1994 to 2001 and later collected into 18 volumes. It was later adapted into an anime series by Madhouse, which aired from 2004 to 2005 and ran for 74 episodes.

The series follows a Japanese doctor, Kenzo Tenma, who is working as a brain surgeon in Germany. While he enjoys a good position at the hospital he works at, he's not entirely happy with how things are run. When he has to make a choice between operating on a local political figure and an injured boy, he chooses the latter. However, this single choice ends up altering his life forever.

Monster is a series that's best experienced if you know as little about it as possible; it's entirely plot-driven, so I'd rather not give anything away. It's a psychological thriller that will keep you guessing until the very end, with a villain unlike any other.

I personally recommend watching the anime over reading the manga; the anime is a superb adaptation and definitely enhances the experience.