Ring World!

Every choice has thousands of other consequences. When the world suddenly fell into darkness and was submerged by the ocean, the protagonist embarked on a wonderful, terrifying and depressing journey. He met a group of secret workers in the government's shelter "Water Balloon" and learned shocking secrets about time and life, but dangerous creatures also followed one after another. He experienced a broken life, but eventually found that every choice he made had branches and buds elsewhere. All the secrets are in this ring world.