Since I'm not familiar with this exact work, it's hard to give a detailed analysis. However, in many novels with such character - based titles, the end often ties up loose ends regarding the relationship between the characters. It could be that the 'denpa onna' and the 'seishun otoko' have a final encounter or realization. Maybe there are revelations about their true feelings, or they come to understand something about themselves through their interactions. It could also be that the end of the novel sets them on different paths, showing how their individual growth has led them to different futures.
I haven't read this novel specifically. But generally, it might explore the relationship between the characters, perhaps with themes of youth, identity, and unique personalities. Maybe the 'end of novel' part implies a conclusion to the story arcs of the denpa onna (a girl with some special or 'radio wave' - like characteristics) and the seishun otoko (youthful boy).
The 'denpa onna to seishun otoko end of novel' could potentially be about how the two main characters have changed throughout the story. It could show their growth, or the resolution of conflicts that were present between them. The 'denpa onna' might have her own quirks that have influenced the 'seishun otoko' and vice versa. And at the end of the novel, we might see how they stand in relation to each other and to the world around them.