The The Rising of the Shield Hero.

  Iwatani Naofumi, a run-of-the-mill otaku, finds a book in the library that summons him to another world. He is tasked with joining the sword, spear, and bow as one of the Four Cardinal Heroes and fighting the Waves of Catastrophe as the Shield Hero. Excited by the prospect of a grand adventure, Naofumi sets off with his party. However, merely a few days later, he is betrayed and loses all his money, dignity, and respect. Unable to trust anyone anymore, he employs a slave named Raphtalia and takes on the Waves and the world. But will he really find a way to overturn this desperate situation?