Each player is being asked to contribute $2500 towards the $70,000 trip. The team is advertising nationwide for assistance.
Apart from visits to his country of birth, Tonga, it will be the first overseas trip for Tupou, who was named in the Hurricanes under-16 tournament team earlier this month. He has been in Hawke's Bay since he was 8.
Tupou is aiming for a career as an architect when he leaves school.
"Academics are pretty important to me. I'm pretty focused on preparing for my level one exams at the moment and then it will be back to the fundraising. I don't mind if it's orchard work or any other kind ... as long as I raise the money to make the trip," Tupou said.
Prop Mosese Fineanganofo is in a similar situation to Tupou. Once his Year 12 level two exams are finished he will take on whatever he can to raise his share of the funds.
"Obviously winning the National Top Four title was pretty good. But helping the school win a world title would be more special."
A former Tonga under-15 and under-16 rep, who started playing rugby as a 10-year-old, Fineanganofo arrived at Hastings Boys' at the start of the year from the Tongan capital, Nuku'alofa.
He is also good academically and the fact he is prepared to go to university and study civil engineering while chasing a Super Rugby career reflects that.
"By appealing nationwide for assistance we're hoping former students involved in the corporate world might be able to help," team manager and former Magpies halfback Jason Bird said.
"We know familes have been hit pretty hard with fundraising lately and we knew if we just kept it in house the same people would be targeted again and that would be tough. At the same time our players are prepared to do orchard work and farm work as part of their fundraising so they're not just waiting for hand outs."
The 28 players selected for Japan will include 17 of the 23 players used at the National Top Four tournament last month.
The touring party will leave Hastings on April 26 and return on May 6. When HBHS played at the tournament last year they reached the final before losing 35-5 to Fiji's Ratu Kadavulevu School.
Anyone interested in sponsoring a player's trip or with work opportunities can email HBHSadmin@xtra.co.nz to get more information.