Like Canada, they've been ever-presents as the leading Asian nation, but once at the tournament, it's often been grim viewing.
Alongside 18 defeats, they have managed a solitary win, 52-8 against Zimbabwe at Belfast in 1991, and a draw against Canada four years ago.
Some defeats have been avert-the-eyes occasions.
Their 145-17 spanking by the All Blacks at Bloemfontein in 1995 hurtles to mind; or the 91-3 defeat against Australia at Lyon four years ago.
So Kirwan, now in his fifth year at the helm, has his hands full.
But he's optimistic.
"I think if we can get there and play incredibly competitive games against France and New Zealand, and then play Tonga and Canada, we will show the world how much Japanese rugby has improved," he said.
His backline will include former Auckland and Northland first five-eighth James Arlidge, and Otago midfield back Ryan Nicholas and provincial B lock Justin Ives, among 10 foreign imports, with other players from Tonga, Australia and Samoa.
"We need to use the foreign players to help our country get better," was Kirwan's rationale.
The Japanese strengths? Pace, fitness and quick hands and piles of enthusiasm. Weakness? Sheer bulk, as usual.
They'll miss their leading international tryscorer, Daisuke Ohaka, who has retired with a knee injury. First five-eighth Ryohei Yamanaka has been ruled out apparently on account of a dodgy hair tonic, rumoured to be aimed at helping grow his moustache, but which contained a banned substance.
The 31-year-old loose forward Takashi Kikutani will captain the "Brave Blossoms" at the cup.
Look out for flying winger Kosuke Endo, who scored a couple of fine tries four years ago and had a few games for Canterbury in 2008.
Fixtures:
Pool A
Saturday September 10 v France, North Harbour Stadium (Auckland)
Friday September 16 v New Zealand, Waikato Stadium (Hamilton)
Wednesday September 21 v Tonga, McLean Park (Napier)
Tuesday September 27 v Canada, Napier (McLean Park)
