Some time ago, a rare sea ore known as "sea sapphire" was discovered beneath an island due to its unique hue. It was highly valued as an eco-friendly energy source, and a prison was erected on the island to extract it using prisoners. It was later discovered that prolonged exposure to the ore caused a significant transformation known as "indigopathy," which led to the establishment of a research facility to study it. The prison was then replaced.
During this time, an unidentified patient woke up on a table with no memory. A girl with blue hair, arms, and legs crashed through the wall and rescued him. The girl called him "Kai," and he was amazed by her appearance. She encouraged him to follow her and escape the island together, reminding him of a promise he had made.
