The Japanese teenager came on for the final 20 minutes of the 3-1 league cup win over Shrewsbury Town at the Emirates Stadium and he told the club's official website that it was a great feeling to achieve his dream.
"It has been my dream to play on the Emirates pitch, it's great and I am really happy," Miyaichi said.
"One year ago I was still in Japan and playing high school football. I didn't even think I would be playing here so it was a surprise. I was working hard and now I am here I have to keep my feet on the ground and try even harder."
He added: "It was a mixture of nervousness and being excited [before coming on]. I could hear the crowd before and then I got a bit more nervous.
"I could hear the calls and I was really happy. I wanted to respond by playing well and hopefully that can lead to the next step."