Isekai Shoukan wa Nidome desu

When the world of Eclair faced catastrophic peril from a brutal war waging between the human, beastman, and demon races, a lone man was summoned to intervene. Fulfilling his mission, he successfully saved the realm and returned triumphantly to the human kingdom. However, his reward was betrayal; fearing that the immensely powerful hero would usurp his throne, the human king orchestrated a malicious trap. Caught in this conspiracy, the hero was subjected to a transfer spell that reincarnated him as an infant in modern society. Sixteen years later, he navigates high school under the identity of Suzaki Setsu. Though branded as a gloomy, bookish outcast who endures bullying, he remains entirely focused on finding a way back to the fantasy world he once left behind. His perseverance pays off when he is suddenly summoned to Eclair once more—this time alongside his entire high school class by the human kingdom. Uninterested in repeating the past, Setsu declares the renewed conflict troublesome and slips away from the human nation. Arriving five years after his original departure, he sets out to reunite old acquaintances, including the former demon king and the beast king. Unfortunately, his plans for a quiet journey are continually derailed as he finds himself entangled in fresh, sinister plots, following the misadventures of a former hero completely lacking in motivation.