He says his father, now 69, is still coaching rugby in Japan and keeps in touch with friends in Christchurch, having visited them shortly after the February earthquake.
Despite the efforts of New Zealand-inspired enthusiasts like his father, and countless New Zealanders who have played professionally there, rugby in Japan made little progress in the 40 years after that first tour.
Admitted to every World Cup, Japan were last night looking for just their second win in seven tournaments.
This time a new spirit is evident, an attitude that Hiroshi Sakata attributes to "JK".
Kirwan finished his playing years in Japan and was appointed coach before the last World Cup. Sakata says Kirwan has done wonders for the mental preparation of the team for this cup by invoking the "bushido" (samurai) tradition.
Helpfully (or not), a team media guide explains that Kirwan has introduced the story of one of medieval Japan's greatest warriors, Musashi Miyamoto, in a famous battle with a rival, Kojiro Sasaki.
"Musashi carried only a wooden sword," the story goes, "but the duel was short[ly] settled. Masashi had waited for the sun to get in the right position. After dodging a blow, Sasaki was blinded by the sun. Musashi struck him on the skull, killing him.
"The Japanese national team draws inspiration from Musashi's achievements, and also strength from his message: winning is not only found in physical or technical ability."
Tonga have no such media guide. In fact their media contact is now the team manager after a late resignation. Aminiasi Kefu is also Tonga's Solicitor-General and says he is keeping up with official work by email while looking after the World Cup team.
Of the 30 players in his squad, only one lives in Tonga. He says eight live and play in New Zealand, the rest in Europe or Japan.
He is speaking with a sniffle. Even the overseas boys are feeling the cold, he says.
To satisfy keen support in Tongan communities the team have spent hours in church. A Tongan service, Kefu explains, can take an hour and a half, followed by a lunch that can last as long again.
Today they head for the Bay of Islands to prepare for their final pool match, against France. This is the one they have targeted from the outset, he says quietly, a smile giving just a hint of a Tongan surprise.