Re:Birth Colony - Aokage no Azurite  

Rebirth Colony - Azurite Blue Shadow, Re：birth colony -蒼影のアズライト-

Five centuries ago, an event known as the 5th Star Rain caused global temperatures to drop significantly, leading humans to seek refuge in underground habitats, underwater communities or large man-made structures called arcologies. Initially, people hoped for the day when Earth would return to normal, but over time they became disinterested in the outside world and contented with their small, peaceful existence within these enclosed environments. The Aquarius Arcology was established as an international research facility on a man-made island, but it has since become a divided city with distinct wealthy and impoverished areas. Souji, an orphan living in the poor section of town, owes his life to a blue-haired woman who saved him and his sister Ruri. Unfortunately, she disappeared one day, leaving Souji helpless to save her. Driven by a desire for revenge and to become stronger, he vowed to protect those around him. One day, a mysterious girl appeared before Souji. She looked identical to the missing woman and shared the same name - Azurite.