Fate/stay night

 Raised by a mysterious sorcerer after the death of his parents in a catastrophic fire, Shirou Emiya has only just begun to learn small tidbits of magic. When he is caught in a battle between two powerful Magi, however, he ends up performing a spell above his expected ability, accidentally summoning a beautiful woman knight to protect him.

Shirou is thus unwillingly thrust into the competition known as the Holy Grail War where Seven Magi called Masters, together with their spirit partners called Servants, fight to acquire a powerful artifact said to grant every wish.