TOKYO—Japan is preparing to reintroduce the teaching of traditional Japanese ethics in schools, as the nation’s conservatives seek to restore the values they say were rooted out during the U.S. occupation after World War II.

The education initiative is part of an effort by Prime Minister Shinzo Abe and his conservative allies to push policies meant to cast Japan as a stronger, prouder and forward-looking country, one less apologetic for its history. That new assertiveness has sometimes provoked Japan’s neighbors and riled...