The 23-year old Japan international has been signed from German champions Borussia Dortmund and plans to continue his rapid improvement at Old Trafford as he prepares for the 'greatest challenge of his career'.
"I'm happy to be here and every day I'll take the chance to improve myself and move further up," he told reporters.
"It's definitely the greatest challenge of my career and I hope to learn and improve every day.
"I've always said I have to improve my playing qualities; now I've been here a bit I can really feel the difference. It's a top level club and environment, and when the other internationals join us it will be even better.
"Everything here shows me it's a really big club and it's a great honour to play here. I want to really contribute by achieving concrete results."