Oita Saikyou no Shuujin wa Kyou mo Ikinokoru

In the jail known as Solitude of Karaisman, trillions of prisoners are kept in brutal conditions. Somehow, a blind man named Argel Lastos has survived for decades, despite being one of the prison’s first inmates. Now, he’s determined to protect and train a child named Cero to turn his unrealized talent into a fearsome power, all while defending his friends from the desperate inmates. But, is the old man only doing it to save Cero… or is it for a far more sinister purpose? (Source: Tapas)