He was mobbed wherever he went on United's tour of Japan, but they already know he's a star in his homeland.
He scored against Cerezo Osaka, his former club, but they are well aware that he has a habit of popping up in the right place at the right time.
What they don't know is what the new season holds for the midfielder signed from Borussia Dortmund a year ago, or where David Moyes sees the 24-year-old fitting into the team post-Sir Alex Ferguson.
This time last year, the arrival of a player who had won the Bundesliga twice in succession was seen as a coup.
But it was soon over-shadowed by the signing of Robin van Persie from Arsenal.
It was as if United fans had been given a BMW for Christmas, only to be handed the keys to a new Ferrari an hour later.
And so followed the rest of the season.
Kagawa looked bright and sharp on his debut at Everton, but the talk afterwards was about Van Persie's first game in United red.
He scored on his home debut against Fulham five days later, but Van Persie had already done the same. And in rather more spectacular fashion.
The problem that Sir Alex faced last season was how to fit Kagawa, Van Persie and Wayne Rooney into the same team.
And not only fit them into the same 11, but get them playing in their best positions.
Van Persie likes to play as a centre forward, but so does Rooney.
Rooney likes to drop into the hole, but Kagawa likes to play there, too.
When Van Persie and Rooney were picked as a front two, Kagawa was often played out wide or left on the bench.
And when all three started the Champions League quarter-final with Real Madrid in the Bernabeu, Van Persie and Kagawa played in their preferred positions but Rooney was forced to do a job in midfield.
Of the 54 games United played last season, they only started together eight times.
Injuries played a part with both Kagawa and Rooney spending time on the treatment table, but it's still an odd statistic. For the record, of those eight games, United won six and drew two.
It's a problem Moyes has inherited from Sir Alex, the one downside of taking over a squad packed with world class players.
Of course, the issue goes away if Rooney leaves Old Trafford this summer.
Moyes's stock formation at Everton last season was 4-4-1-1 with a link man behind a lone striker and Kagawa's movement, touch and passing make him well-suited to being Van Persie's creator in chief.
But if Rooney stays and is partnered with Van Persie up front, or given a deeper role, Kagawa could again find himself in and out of the team as he was last year.
There is no doubting Kagawa's ability, it was plain to see at Dortmund and in those first few touches at Goodison Park.
But where he fits into a team that includes both Rooney and Van Persie is not so obvious.
It's one of the more welcome problems Moyes will face as United manager. But one he still has to solve.
Rob Dawson is Bleacher Report's lead Manchester United correspondent and will be following the club from a Manchester base throughout the 2013-14 season. Follow him on Twitter @RobDawsonMEN