Kami no Tou (Dub)

Tower of God centers around a boy called Twenty-Fifth Bam, who has spent most of his life trapped beneath a vast and mysterious Tower, with only his close friend, Rachel, to keep him company. When Rachel enters the Tower, Bam manages to open the door into it as well, and faces challenges at each floor of this tower as he tries to find his closest companion.

(Source: Wikipedia)