This series is a frustratingly slow-paced series, a combination of strange futuristic spirituality and science fiction. At the same time, it's so short that you run through it quickly. Most of the series you spend getting to know more about the culture and its background, and then toward the end you finally start getting to the heart of Kai's connection to Marie and Pipi's connection to Kai. The series has strange plot twists involving these three.
The main character is actually Pipi and not Kai, which you'll understand very clearly at the end.
There are a few truly odd scenes:
Kai masturbating to the thought of Marie, but I wonder how accurate this scene is, due to the ending plot twist... and Pipi and Kai in the flashback scene in the last chapter when Kai reappears from the ocean--I won't spoil it though
The ending was pretty surprising, but I was satisfied by it. And a little depressed. And amazed. And confused. All in all, it's pretty good, but pretty weird. If you want something happy, upbeat, and hopeful, I wouldn't look here. It's not depressing, but it's not... uplifting, either.