"The big difference between junior and senior levels is the timeframe each team has to prepare.
"Juniors have weeks, while our seniors will have 30 minutes with only pen and paper to prepare, once a motion is announced."
The competition itself could be "a real pressure cooker situation", Thrasyvoulou said.
"Debating is like an intellectual sport, in a way.
"I think it's different from other sports because, after the debates, it's really collegial. There's lots of handshaking and talking about how good the other team was.
"When the decisions come in, the winners are almost embarrassed. Everything is really friendly."
Debaters compete in five limited preparation debates over the two-day competition. After the five rounds, the finalists are decided through a combination of total wins and individual speaker points.
In senior competitions, teams also have the chance to interject into a rival's speech to ask a question, through the use of a POI (point of information).
Topics on Sunday included performance pay for teachers, the effectiveness of protest movements such as Black Lives Matter, and whether Peter Pan should have stayed in Neverland.
Team member Bridget Jones Long (Year 12) said that last topic had been the most unexpected.
"For something like that, you have to try and apply it to a real-world situation," she said.
Team leader, Year 13 student Mia Perkins, won the Cross Cup for best speaker in the region for the second year in a row.
"The topics are generally pretty broad," she said.
"It could be healthcare, pacifism, social movements or something completely different. Having a good general knowledge and inference really helps you in loads and loads of debates.
"Being a good debater comes in handy when you're dealing with your parents as well."
Elliot Jones (Year 12) said working together and "sharing your knowledge around" was important for a successful debating team.
"You obviously know a little bit of stuff yourself, but others in your team might know much more about other certain topics.
"It's about helping each other out as much as you can."
Thrasyvoulou said one of the highlights for him was getting a hug from one of the coaches of the Whanganui High School team after Collegiate took out the top spot.
"They said they were pleased the trophy was staying in Whanganui.
"It really meant a lot, because we've been trying to win this one for a while now."
The Central North Island team that will go to the nationals in May is made up exclusively of Whanganui students. They are Mia Perkins, Bridget Jones Long and John Bryant, with reserves Elliot Jones, and Alice Quigley from Whanganui High School.