Anime in which a boy who follows a goddess and has some fire ball powers. The powers are like images on his back which only the goddess can read. He goes into the tower to kill monsters which turn into crystals with size proportional to the monster's size and the number and ferociousness of monsters increases by levels in the tower. He then collects the crystals and sells them for more weapons and takes care of her goddess. There is one more female warrior in front of whom he always faints and she saved him a lot (romantic angle).
This is DanMachi, also known as "Is It Wrong to Try to Pick Up Girls in a Dungeon?"
Bell has a goddess who is in love with him and only has him in the guild. The goddess (Hestia) can read his stats on his back and power up skills.
Not only the goddess can read these stats but everybody who has access to his back if they have the blood of a god or sufficiently powerful magic.
Bell falls in love with the legendary 'Sword Princess' (Ais Wallenstein) and tries to follow in her and her familia's footsteps to be a great dungeon clearer. He is saved by her when he wanders too far into the dungeon.
Life in the bustling city of Orario is never dull, especially for Bell Cranel, a naïve young man who hopes to become the greatest adventurer in the land. After a chance encounter with the lonely goddess, Hestia, his dreams become a little closer to reality. With her support, Bell embarks on a fantastic quest as he ventures deep within the city's monster-filled catacombs, known only as the "Dungeon." Death lurks around every corner in the cavernous depths of this terrifying labyrinth, and a mysterious power moves amidst the shadows.
Even on the surface, survival is a hard-earned privilege. Indeed, nothing is ever certain in a world where gods and humans live and work together, especially when they often struggle to get along. One thing is for sure, though: a myriad of blunders, triumphs and friendships awaits the dauntlessly optimistic protagonist of this herculean tale.