beta
Child trafficking or a sindicate.
The infinite blue can be a metaphor for freedom that the children being kept there yearned.
The book may be a journal passed by the former 'oldests' to the next ones that can literally be seen as a journal of what they wish to achieve, or a record of their emotions, however it can also symbolize generational trauma passed down.
What's cool about the journal is that the parallelism of Kazu-nii reading the journal in the 1st few panels, him writing on it in the middle part, and lastly handing it down to the next.
It's as if saying that, they still have a choice to rewrite wht they want to happen if they want to change things, because the journal can still be filled with words.
If the journal was full it may symbolize a generational trauma that will repeat its cycle, but so blank pages can mean hope for a change if someone would just take it.
Lastly, idk if i should point it out but i think these children are raised normally with good food and clothing to raise their worth in the market. The purer the innocence the better tainting kinda mindset. 17 i think is also the peak for the children's body, maturing bodies still with the features a child so, ig whoever the sindicate's leader is, is a sick fck who should burn in hell