I think the whole anime can be summed up by saying it is a beautiful story of characters - both children and adults - wrestling with those exact questions: What is an adult? When did I become an adult? Much of the emotional weight hangs in the tension of trust between child and adult, and the show spins an amazing web of balancing tensions: uncomfortable and hilarious, love and hate, young and old, competition and companionship. No matter how much I tried to convince myself that this is just a random loli anime, I couldn't help but feel for the main characters. Kokonoe and Aoki are both very relatable characters in challenging situations with arcs that only resolve after a lot of wrestling both externally and internally. Even Reiji and Kagami, secondary characters, see some resolution to their character arcs.
My only disappointment is that Usa and Houin (and maybe Shirai) don't really ever change. They all get a decent amount of character exposition, so it feels odd that they never really develop much. Also while I love the character arcs and how they resolve, I think there could be more nuance, considering the show feels like it wants to be more of a high drama than a kids show. But perhaps that in itself is another tension of trying to be understandable to both children and adults.
The show really captivates my attention because the situations presented are actually very real. Humans all come from messy backgrounds in one way or another, whether child or adult; and the trust that we have lost with each other always eventually comes to the surface, whether consciously or not. And when your trust is being tested, how will you respond?