Boys' High will start their campaign on Thursday against Kokugakuin University Tochigi High School, then take on Iwami Chisuikan High School the following day and, after a rest day, face Jianguo High School on May 1.
Simpkins has done what homework he can on the opposition.
"Definitely we've had a look at a few YouTube clips, but at the end of the day, I know what to expect from Japanese rugby. They are getting better and better. They are hard, fast, really accurate at the set piece - we are definitely not taking them lightly and that's been the message all the way through the campaign - there are going to be some tough battles, and we have to give them respect."
The team will be led by captain and No8 Matangireia Yates Francis, halfback Te Ra Whata and first-five Kaleb Trask.
Manager Bruce Buckton said the high school's rugby success was, in many ways, down to the appointment of Simpkins as director of rugby in October 2014.
"That takes the pressure off the teaching staff - prior to that, it was on the shoulders of teachers and, although we were happy and we enjoyed doing that, if we wanted to reach that next step we had to think about that opportunity to look at having a full-time position for someone who could develop rugby right through from Year 9 to 1st XV."
At the time of the appointment, the high school had a good crop of under-15 players and many of them are now part of the squad travelling to Japan.
There was limited time to prepare for the Japan tournament, the school's place having only been confirmed in October.
"For a tour that you know is coming, you can plan 18 months out and fundraise and give parents notice. Obviously there is a cost to this [Japan trip] to families and they've been fantastic at getting that together so quickly."
Simpkins said the players were well aware of what was resting on their shoulders as they headed to Japan.
"We've got an expectation that we are representing our school, New Zealand and our families and we are really looking forward to that challenge and the boys have been working hard and hopefully putting New Zealand on the map."
The tournament final takes place on May 5.