The Trials of Chiyodaku, Vol. 1 (novel)

Akuto, a normal game-loving highschooler, and his older sister Tsukasa are summoned one day to a strange otherworld called Chiyodaku. There, a laidback princess tasks them with becoming judges for her kingdom and assigns them a difficult first case—a murder trial with a hero as the accused! Akuto must help his sister, who knows nothing about fantasy worlds and their logic, navigate eccentric courtroom characters as the siblings pursue the truth, no matter where it leads.