The 26-strong Irish squad were put through their paces today by head coach Niall O'Donovan and assistants Michael Bradley and McCall on the artificial pitches at the Osaka University, on the outskirts of the city.
Following defensive drills early in the session, McCall admitted: "With the speed that Japan have in their backline, you certainly cannot afford to be placing loose kicks in around their back three.
"They love to run from deep and are exceptionally quick, so it is an area that we must be wary of."
McCall's first involvement with the Irish senior set-up has gone down a treat, and the former international centre reckons the players, old and new, have knitted together well as a tight squad, especially with 12 regulars missing due to the Lions tour, as well as long-time number 8 Anthony Foley.
He said: "From my point of view, the players all work with similar defensive systems in their own provinces and clubs, so it's a case of ensuring that they are all comfortable with the Irish system for Sunday.
The players have all worked well together and we are all looking forward to the first Test with a degree of eagerness."