Wenger handed the Japanese starlet a start against his former club on Monday, and the 20-year-old restored his faith with a fine penalty in the first half.
Miyaichi has been linked with a second loan move to Eredivisie outfit Feyenoord in recent weeks, but Wenger suggested that he wants the midfielder at his disposal next season.
|10/1||Arsenal are 10/1 with BetVictor to win the Premier League
"He just needs to come back to full fitness and then the rest will come along. His pace, his mobility and his movement off the ball.
"I like players who can move when others have the ball. There is also his attitude, commitment and desire. That is why I decided to keep him."
Olivier Giroud scored his sixth goal of the pre-season tour and won Arsenal a penalty, which local favourite Miyaichi stepped up to score, before Theo Walcott found the net.
Wenger says he was pleased with Arsenal's performance and that his side are starting to look promising ahead of the new Premier League campaign.
"It [the penalty] was not planned. When Ryo scored I thought it was a good decision from [Mikel] Arteta," he added.
"It was a game played at a good pace. Of course it was a special event and the stadium was full. We played with greater fluency, especially in the first half, and we created chances.
"We played with good focus and a good attitude. At this moment of the season we look quite sharp."