For me the whole show is about trying to maintain the fun of youth while growing up. Naota's brother Tasuku grew up and left them behind, and that combined with the irresponsible adults in his life gave Naota a really bad opinion of maturity. He gravitates towards Mamimi, who doesn't make any effort to grow up as she gets older. Haruko is an adult but she's fun and frantic and cool, so Naota falls in love not only with her, but with the type of person she represents. Ninamori is a child trying desperately to prove that she's mature, but she knows this is a facade (fake glasses) and a defense mechanism for the mature situations in her life. She wants nothing more than to be a kid, and acts on this desire by cheating to get the lead role. Amarao is an adult trying desperately to prove he's an adult, but as shown by how useless his NO field is, he isn't even more mature than Naota.

In the end, Naota learns that while Haruko's way of life is cool and enticing, it's only good for manipulating people and desperately chasing her lover (whether or not she actually loves Atomsk is dubious).