I read this light novel series like 5 years ago and recently came upon it again.
If you are looking for great complex characters, a wide diversee cast, an intriguing, unpredictable plot, this is the series for you.
There's 13 books in the series but since it's a light novel series, it isn't as heavy as a standard novel.
It's the rare genre of Urban Fantasy, meaning people live in a normal city, Japan's Ikebukuro with normal lives but there's supernatural incidents behind the scenes. For example there's a woman without a head, a demon blade, etc.
The interesting thing is that the characters all have their own secrets and agenda, so it makes for a lot of twists and turns into the city's story.
Made into an anime as well but the light novel goes much more in depth.
Also the 'antagonist' Orihara Izaya is so popular there's a wikihow on how to be like him lol. His name means 'The One Who Watches Over The Crowd'. The author writes with thought and care, putting thought into the characters' names.
Anyway it changed my life cause I started doing character analysis because of this and was able to express my thoughts and feelings about the story and characters honestly.
Like, it's kind of like Harry Potter in terms of characters? They're all so diverse complex and interesting that you can't forget them even after you finish the series.
And the characters are what makes an exceptional story.