A clash against the big-hitting Pacific Islanders launches England’s World Cup quest in Sapporo on Sunday in what will be only the third meeting between the rivals and their first since France 2007.
Itoje has played alongside the Vunipolas at Saracens for six years and since 2016 has operated in the same England pack, leaving a lasting impression of the ruinous impact the brothers of Tongan heritage can have.
“I’ve seen what those two have done to people! It can be dangerous if you allow it to be,” Itoje said.
“We know how physical they are and how much Tonga as a country love rugby. They’ll definitely be up for it.
“We know that they’re an incredibly physical side. From one to 31 they have big boys who are physical and aggressive. They have huge athleticism as well.”
Itoje was speaking at England’s official welcome ceremony in Miyazaki where players and coaching staff received World Cup caps presented by Bill Beaumont.
After a 10-minute display of taiko martial arts drumming, Billy Vunipola was invited on stage to take part in a Daruma eye-painting ceremony during which he was asked to make a wish.
Vunipola said: “I wish that whatever we do in the next few weeks will live with us for the rest of our lives.”
The number eight then painted in one eye on the Daruma doll before the players gathered for a team photo.
Scrum-half Ben Youngs was also presented with a devil’s mask as a gesture of good luck.
“I’m incredibly excited that we’re here in Miyazaki and I can’t wait to get started,” said Itoje, who gave a speech in Japanese.
“Every day in the World Cup process I’ve been involved in so far has been a little bit different. I’m in a completely new and fresh country with new experiences every day.
“There are different people, different culture and a different lifestyle. I’m living it day by day and am enjoying it as much as possible.
“There’s a good feeling at the moment. This is the longest period of time that the squad has spent together for an awful long time.
“You can tell the whole squad feels together and that we’re building towards something. We feel as if we’ve grown tighter and more cohesive. The feeling is good.”