In episode 5 of Kyoukai no Kanata, Akihito is reading a book while he skips school:
What is this book?
Though it's a little bit difficult to read since his fingers are covering the spine, this book looks like Two Billion Light-Years of Solitude (or 二十億光年の孤独), by Shuntarou TANIKAWA.
Two Billion Light-Years of Solitude is a collection of poetry - in fact, Tanikawa's first publication, published in 1952.
