Symbolism or whatever you want to call it. These manga speak volumes behind their images of what is happening and what could have happened. The boy might have ignored her, but he didn't; The girl could have been more sincere, but she didn't; The boy could have committed suicide, but he made the decision to hit his attackers, etc. Now to understand it in a simple way, The boy in the 1st chapter caught a USB memory, the girl, even though she was close to the sea, never caught anything. Can you imagine these two protagonists in a different setting? They could have been kissing at the seashore like two young men who met each other
(symbolically they appear at the end). But the setting is different, the seaside or adolescence is not the same for everyone, some are lucky to find something soon, others go round and round to get out of this complicated shore. Works that call for reflection and leave you that sour taste because they appeal to your circumstances as a person that led you to act in such a way.

PS: The first impression I had of the girl was "wtf this ugly", I thought it was a bit mediocre for art, but then I saw the backgrounds and knew it was part of the symbolism of the character's development, they noticed that every time the chapters the girl was prettier? ... that certainly is something I had not seen in another manga, or I do not remember, having done that on purpose to symbolize the beauty of a character while you develop it, gives an extra point to my opinion.