The Japan midfielder feels he's improving as a player training with his teammates.
"I really feel that we have a strong ability to bounce back when we are behind, so people in this team must be really mentally tough," he said.
"We have a really strong squad with many world class players, so it's lucky for me to have opportunity to train with them and play games with them.
"Sir Alex is one of the best managers in the world. What I am really impressed are the numbers of great players he has helped to grow, the numbers of titles he has achieved for the team almost every year, and his ability to mould top players into a team.
"Also, the atmosphere supporters make at Old Trafford helps the team to fight back. As I said, my team-mates are so experienced and mentally strong as I said.
"I'm really lucky to play with world-class players and experience those things, including the history of Manchester United."