Gloomy, shy, and desperately awkward—Itsuki spent years training under the belief that being strong would make him popular. He eventually earned the title of the "World’s Strongest Assassin," yet he remains completely alone. "I dont care about being powerful anymore; I just want normal friends!" One day, a chance encounter during a mission leads him to Emilia, a saint who is just as socially stunted as he is. As they form a party, a shocking truth comes to light: Emilia is actually his long-time pen pal! Before long, his other pen pals—a genius mage and a legendary alchemist—catch wind of the news and join the fray. But there’s a catch: despite their top-tier specs, every single one of them suffers from severe social anxiety. Thrilled to finally have a group of friends, Itsuki and his party try their best to complete quests without drawing attention. However, theres no hiding the fact that a "Rank E" party is slaying Rank A monsters and capturing ultra-rare creatures. With an unprecedented rise through the ranks, Itsuki’s quiet life is about to get a lot more crowded as the Guild, local lords, and the Royal Knights all turn their eyes toward this group of overpowered misfits.