Based on the excerpt, what conclusion can readers make about the relationship between Neptune and Ulysses?

If taken out of context, the characters, yes, could seem a bit too idealized to be believable. However, the characters in any story should be considered on par with all a story’s literary elements.  For instance, the story takes place in the distant future after a great war where there is a great deal of brainwashing of people that has taken place.  With all that in mind, it is understood that pretty much anything can be possible, which makes the characters—as idealized as they may seem to some—all the more believable.