MONSTER by Naoki Urasawa is, far and away, my most favorite anime I've ever seen. It is based on the manga of the same name, and the story is just incredible. Before I say anything more, I recommend watching it, its wonderful.

I'm not really interested in giving a plot synopsis as that can be searched for, I would rather to discuss my thoughts on it and what makes it my favorite anime. A problem I personally encounter with some anime is the weirdly perverted elements which are just kinda, there. Some are able to use it in a way that makes sense despite the cringe (e.g., Shinji is growing up and dealing with a lot in evangelion), others simply include it just because? (e.g. gurren lagan which was genuinely insufferable). Now listen, I don't want to be a prude or puritan, it just has a tendency to be portrayed in younger characters that just makes it feel gross to be watching as an adult. I digress, I bring this up as MONSTER does not fall into this trap. It takes its story and stakes very seriously. The only instance of sexually charged content is when some random dude is with a prostitute and a 10 year old is walking by, sees it, and is traumatized (this is a simplification, watch the anime). This is kinda at the core of why I love it, because it takes itself seriously and does not play something off for laughs. The content is heavy and introduces such interesting moral dilemmas, down to the core plot.

Dr. Tenma, the highly talented neurosurgeon, sticks to his personal morals and decides to perform life saving on a kid who had a bullet in his head instead of operating on the mayor. The mayor ends up dying, and Tenma has his career set back. The surgery was successful for the boy, whose name is Johan. Dr. Tenma, after being told he'd be passed up for a promotion and his fiance breaks up with him, goes on a rant to the unconscious Johan. He is aggrevated by the higher ups being more interested in money than saving people's lives, and prioritizing people who are simply of higher status. In a fit of anger, he wishes they were dead(if memory serves). Some time later, the director and other related workers have been found murdered, and while everyone (wrongly) suspects Tenma, he is never charged for anything.

Years later, his career picked up again, becoming the chief neurosurgeon at the same hospital. He operates on a patient who is a criminal warning of a "monster" (Junkers). True to his character, he misses a date in favor of giving this patient a gift. However, when he returns, The guard is dead and the patient is missing. He tracks him down to a construction site, finding Junkers being held at gunpoint by Johan. Tenma tries to plead not to kill him, but Johan executes Junkers. Before leaving, he tells Tenma that he wouldn't hurt the person who saved him. It is here that the core moral dilemma of the entire series reveals itself; the nature of healing people without knowing what they may become.