For the biggest part of Kokoro I felt like I was missing a lot of it. It is of course my own fault for not realizing it was a sequel before getting the book, but still this is one of these books I would certainly not recommend reading as a stand-alone as you will probably feel as lost as I did.
It's presented as a combination of Japanese folklore and science-fiction, and at times it felt like I was reading a manga (without the pictures), but the story moved incredibly fast and was at times a bit overwhelming. Due to this, I never really got invested with the characters, either on Higo or on Earth. If I had liked Kokoro better, I would have certainly checked out Kojiki too, as I would have like to see how it all started, but as it stands, I'm rather hesitant and think I'm going to pass.
Thanks to the publisher and Netgalley for providing me with a free copy of this book in exchange for an honest review!