During his trial at Arsenal in the summer of 2010, Miyaichi impressed the Arsenal manager, Arsène Wenger, signing a professional contract on 31 January 2011. Wenger said: “We’re delighted that Ryo Miyaichi has joined us. He trialled with us in the summer and has raw ability which has attracted many clubs around the world”. He was then loaned to Feyenoord, Bolton Wanderers, Wigan Athletic before he returned to Arsenal and he made his UEFA Champions League debut on 28 August 2013 in a 2–0 win over Fenerbahçe. Despite interest from former club Feynoord and SC Heerenveen, upon 1 September 2014 Miyaichi was sent on a season long loan to fellow Dutch side FC Twente. During that season he made 10 appearances in the Eredivisie with the club’s first team. Miyaichi also played 14 Jupiler League games with Jong Twente, scoring three goals and delivering one assist. He returned to Arsenal at the end of the season when his five-year stay at the North London club was brought to an end. Miyaichi has represented Japan from under-15 to under-19 level. He took part in the 2009 U-17 World Cup as a member of Japan U-17 national team. He played 2 matches at the tournament. Miyaichi received his first call up to the senior team for the 2014 World Cup qualification against Uzbekistan in February 2012, though he didn’t feature in the game. Miyaichi made his debut on 23 May 2012 in a friendly against Azerbaijan where he came on as a 60th-minute substitute in a game that ended 2–0 to Japan. He made his second appearance against Brazil to again play as a substitute in a 4–0 Japan loss.