Rud, a shielder with a defense stat of 9999, the highest ever known, serves as a tank for the Hero's Party as they carry out raids in labyrinths. His goal is to find a treasure hidden in one of the labyrinths that can grant any wish, and use it to cure his beloved younger sister's illness... but the tyrannical hero suddenly kicks him out of the party, saying his skill is "useless." So Rud makes his way back to his hometown. Along the way, he saves a young girl, and she reveals the true nature of his skill... which turns out to be incredibly powerful! This is the story of the adventures of Rud, a tank with both the highest defense stat in history and an unparalleled skill!

(Source: Crunchyroll)

Watch Saikyou Tank no Meikyuu Kouryaku: Tairyoku 9999 no Rare Skill-mochi Tank, Yuusha Party wo Tsuihou Sareru Online