"U BOJ!" is very popular song in Japanease glee choir. It is from the opera "Nikola Subic Zrinski" by Ivan Zajc. After the end of the WW I, Croatian mariner's ship sunk in Japan. While they repaired thier ship, "U Boj" becomed very popular glee song in Japan. https://www.youtube.com/watch?v=uqQf_92dgHM