Ayuhara Yorunami wa Yoku Nureru (Volume)

is the first volume of the Ayuhara Yorunami wa Yoku Nureru light novel series, written by Hazuki Minase and Illustrated by Shirai Eiri. It was released under the Dengeki Bunko Imprint in September 2013.

Synopsis
Yohei Nagisa, a boy who drowned in the pool at midnight, noticed that the whole area was on the roof of the school where the sea sank. In that world, I met Ayuhara Yanami, a girl with a jellyfish-like atmosphere floating in the sea. She was an "Undine Warrior" who wore a combat magic costume "Cloak" that could gain more power the more she got wet with water, and fought against monsters ... "Wet see-through action" presented by Hazuki Minase of "C3" has begun!

(source: Bookwalker JP - Translated)