The Rising of the Shield Hero

The Rising of the Shield Hero (Tate no Yuusha no Nariagari) is a popular isekai anime.

Naofumi Iwatani, an ordinary otaku college student, gets summoned from modern Japan into a fantasy world facing catastrophic "Waves" of destruction. Four legendary heroes are called to save it: the Sword, Spear, Bow, and Shield Heroes. Naofumi becomes the Shield Hero, equipped only with a defensive legendary shield (no offensive weapons allowed), which immediately marks him as the "weakest" in the eyes of others.

Things go south fast—he's betrayed, robbed, falsely accused of a serious crime by someone close to the royal family, and left penniless and despised by nearly everyone, including the other heroes and the kingdom. Distrusting people, he buys a young demi-human slave named Raphtalia to fight alongside him, and gradually builds his strength, party, and reputation through sheer determination, clever shield abilities, and protecting those who need it.

The story follows his journey from bitter, cynical outcast to a true hero who rises above the odds, dealing with prejudice, massive monster waves, political intrigue, and eventual growth/redemption arcs. It's known for its darker start, revenge elements, party-building, and progression in a game-like RPG world.

The anime has multiple seasons (starting strong in season 1), and it's based on the light novels/manga by Aneko Yusagi. If you're into gritty isekai with underdog protagonists, it's a solid watch!