1. You realise the world of this manga is fucking disgusting,
2. Then you start to get used to the grime, and you realise every character is fucking amazing and wholesome.
3. Then you realise that this is the point of the manga: You've learnt while the world is bleak and inhospitable, the people living there are still people. Hopes, dreams, loves and aspirations. Beautiful stories behind a horrible exterior. And by growing numb to the setting and empathising with the characters, you've just gone on the same journey that they've all had to go through, to live in that world.
If this isn't masterful worldbuilding I don't know what is
10/10