Ayuhara Yorunami wa Yoku Nureru

Ayuhara Yorunami wa Yoku Nureru (鮎原夜波はよく濡れる) is a light novel series by Hazuki Minase with illustrations by Eiri Shirai.

Plot
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, and fought against monsters ...