Scissor Seven
It's about an amnesiac - Seven - who needs money, so his friend makes him become an assassin. Seven's weapon are scissors he controls with magic. Despite the premise, the 1st season is pretty lighthearted (though there's one S1 episode that was unexpectedly dark). The show's main strengths are characters and plot. There are a whole bunch of side characters, which are still relevant in the newest season, even though it's plot-heavy. Season 4 is going to be released on the 21st this month!
Warnings: murder (duh), suicidal tendencies, mentions of cancer.
Great Pretender
This one's about the (self-proclaimed) greatest swindler of Japan - Makoto Edamura - who gets out-scammed by Laurent Thierry, who's probably the best in the entire world. They end up scamming criminals together.
It has really good animation and a unique art style. There was a lot of thought and effort put into the different languages spoken (in the Japanese version at least) - for example, Laurent's VA for speaking English has a French accent, and the characters who are supposed to speak Mandarin actually speak Mandarin.
Warnings: selling children, murder, abuse, terrorism, trauma, depression, drugs, alcohol, smoking, unspecified terminal disease.
Kotaro Lives Alone
Kotaro is a 4-year-old who moves into Karino's apartment complex. Karino ends up taking care of Kotaro, together with the other neighbors.
The series is largely episodic, with a few multi-episode plotlines. The dark themes and cute things make each other hit harder.
Warnings: child abuse, child abuse victim justifying child abuse, child neglect, death.
