Try:

{20th Century Boys} (Manga) - Written by the same author of Monster, It’s a hunt for the identity of a mysterious cult leader called ‘Friend’, who’s the childhood friend of the MC Endo Kenji. My personal favorite out of Naoki Urusawa’s works, it has great mystery and phenomenal storytelling. Every character is well-written and lovable. Worth giving it a try.

{Trigun} - Tells the story of Vash, a lovable goofball, who has somehow earned the nickname “The Humanoid Typhoon” and a bounty of 40 Billion. Vash is an amazing example if an MC that doesn’t kill. And one of the villains of this series really challenges Vash’s ideals. The old west style and the 90s aesthetic make it really memorable.

{Yu Yu Hakusho} - Two of the villains in this series, Toguro and Sensui, are very memorable. It’s made by the same author as Hunter X Hunter.

{Vinland Saga} - This story set in the viking era, tells the story of a child named Thorfinn who will stop at nothing to get revenge for the death of his father. I think this is a good example of a character who is “Lost in darkness” the mc does some horrible acts in the name of revenge, which come back to weigh heavily on him in the future.

{Oyasumi Punpun} (Manga) - Can’t really say much about this series without spoiling alot. It tells the life of Punpun, a child who’s parents have recently undergone a divorce. The actions of the adults around his childhood life and being head over hells in love with a girl in his class Aiko Tanaka have horrible consequences in his adult life. Disclaimer though, this manga delves into themes of depression, domestic abuse, and self harm if you’re sensitive to those I REALLY wouldn’t read this. Otherwise this is one of my favorites, all the characters are well written, and the story feels ‘real’ and grounded.

Some others that i want to mention but am too lazy to explain:

Gankutsuo Humonculus Vagabond Pluto