 If you liked
Gantz
|
 ...then you might like
Kokou no Hito
|
Both series exclusively centers around the protagonist and their life, there will indeed be a lot of side characters that will occur by itself, their presence will impact the protagonist but they are not all so important to the progression of the story. Similar to Gantz, The climber will start off as a more light and fun series but the more you go through each chapter, it'll get heavier.