Deans' Panasonic Wild Knights will meet Toyota Verblitz - where Hansen is director of rugby - in one playoff on Saturday, while Barrett's unbeaten Suntory Sungoliath will oppose ex-All Black Ryan Crotty's Kubota Spears in the Sunday semifinal.
Neither of the former Canterbury and Crusaders coaching cronies will relish losing to the other, such is their pride and rivalry.
Hansen and Deans were first on opposite sides in schools rugby in Christchurch in the 1970s.
They teamed up to coach Canterbury to a NPC title and coached the Crusaders to the 2000 Super Rugby title, before Hansen left for Wales a year later.
They pitted their wits against each other when Hansen took over as head coach of the All Blacks in 2012, Deans’ penultimate year in charge of the Wallabies. Hansen had the upper hand then, with two wins and a draw in the Bledisloe Cup series.
The four semifinalists feature a wealth of former All Blacks, Wallabies and Springboks as well as handy sprinkling of Japan Brave Blossoms internationals.
Barrett and his Suntory teammates will be fresh for the semifinal after winning their quarterfinal by default when the Ricoh Black Rams - a club including ex-All Black Elliot Dixon and former Kiwi Super Rugby players Michael Broadhurst, Ben Funnell and Robbie Robinson - could not field a team due to a Covid-19 outbreak.
A two-time former World Rugby player of the year, Barrett has already spoken of his desire to win the Japan Top League title – emulating Dan Carter’s feat with Kobelco Steelers two years ago – before heading home to help the All Blacks win the Bledisloe Cup and the 2023 Rugby World Cup.