Honestly the dialogue is a little clunky but I'm sure that is mostly due to some being lost in translation. The film is worth it alone thanks to the stunning visuals. Cannot believe some people don't understand the plot? Its spelled out consistently for the viewer, if anything I think they went overboard with the explanation as just like the setting the timespan is vast and some of the information known by the protagonists is lost and morphed into legend. Yes the characters are also underdeveloped but it fits the premise, its driven by its concept rather than its narrative and does a very good job a doing so. Perhaps the movie is better suited to those who can use a little imagination. I could see a great series or sequel stemming from this film due to the fascinating world building. I will be taking a look at the manga as I need more!