Have you ever watched Babel (2006)?
Different stories, different lives of others, somehow connected by this one event, object, person? This is it. Add to it the story telling of Inio Asano and there you go.
I surely hope this isn't your first manga of his that you're reading or have read because then you might be greatly disappointed: one has to be introduced to this writer by his brightest work and then work their way slowly towards the darker mangas (Oyasumi Pun Pun for example).
Not sure if it's me that hasn't come across such mangas or is it really rare that they are about deeper topics like the ones Asano explores. This is the reason I especially cherish him.
Personally, I didn't like this one so much; probably because I'm fed up with all the dark truths he's throwing at his readers. Yeah, this manga is tagged as slice of life and that's exactly what it is: lives of children who aren't blessed to have a model family, teenagers who have gone through some really disturbing events that cut deep into their personalities, grown-ups that made mistakes that they cannot even begin to fix; mothers abandoning children, dangerous lying, suicide, crime, aimlessness of the early adulthood, pointlessness of life, heaviness of childhood and trying to take that with a certain lightness and humor.