On the Region 1 Kamen Rider V3 6-disc boxset, insert disc 6 and play the "V3 Trivia Quiz".
Answer all 10 questions correctly then push "right" then "up" on the score page to reveal a Shonen Rider pendant. Click "enter" and you'll be treated to lead actor Miyauchi Hiroshi singing the catchy theme song "Tatakae! Kamen Rider V3 (Fight! Kamen Rider V3) at a 30th anniversary party in Hawaii!
Miyauchi Hiroshi laid vocals for the original theme song which plays during the opening of each episode (circa 1973).
Reviews: DVD Talk also has a review of
Kamen Rider V3 by John Sinnott.