While fighting an intense inter-galactic war, a mecha pilot was accidentally warped into a space-time neither he nor the computer of his mecha could recognize. After waking up from a long-time hibernation, he found himself trapped on a planet, with human residents talking in an unknown form of language, using inferior technologies, and -- most shocking to him -- naturally breathable air.
Touya Mochizuki was accidentally killed, and as an apology, God allows him to be reborn in a fantasy world and will grant him any one wish he desires. And so, Touya chooses to keep his smartphone in the next world. In his second chance at life, he befriends many important figures and comes across the world's secret. He inherits the legacy of an ancient civilization and travels around nonchalantly while possessing powers that rival this world's kings.
Long ago, all humans lived in the ocean. But some who longed for the land abandoned the ocean, casting off the special raiments granted to them by the sea god to adapt them to life under the sea...
Though mankind was divided into sea dwellers and land dwellers, each with different ways of thinking, they were all still fellow humans, and they continued to maintain contact as time went on.
Sakishima Hikari, Mukaido Manaka, Hiradaira Chisaki, and Isaki Kaname live in an undersea village, while Kihara Tsumugu lives on land.
When these middle school second-year land and sea dwellers meet for the first time, their hearts begin to undulate like the tides.
The youthful fantasy tale of these young people's lives unfolds in a strange and beautiful world.