McDouall said it was a significant anniversary and the relationship had benefits for the district including regular visits from Nagaizumi school kids to Whanganui.
"It's exciting in a lot of ways to honour a relationship over 30 years," he said.
"To send a good bulked up delegation with seven council people and 11-12 others - which includes my mum, so I'm not going to be getting into any bad behaviour - is really a great symbol of how we value it."
About 10 other delegates will travel to Japan on a self-funded basis but are invited to attend celebratory events and will travel as part of the wider delegation.
The mayors of Whanganui and Nagaizumi-cho signed a sister cities agreement in 1988.
A Whanganui delegation attended the 10th anniversary celebrations of the sister city relationship in Nagaizumi-cho in 1999 and former deputy mayor Dot McKinnon led a small group visit to Nagaizumi-cho to celebrate the 20th anniversary in 2008.
In 2014 former mayor Annette Main and former chief executive Kevin Ross visited Nagaizumi-cho.
A delegation from Nagaizumi-cho will visit Whanganui in January next year and will send a strong contingent to take part in the February 2019 New Zealand Masters Games to be held in Whanganui.