Mikami played alongside Michael Leitch at Tokai University, both joining Toshiba Brave Lupus in 2011. Mikami had established himself as a regular in his university side at Tokai in his just his second year, finishing runners-up to Teikyo University in his third year in the Japan University Rugby Championship.
Mikami's Top League debut for Toshiba came on Christmas Day 2012, coming on as a replacement against Kobelco Steelers on matchday 8. His performances for Toshiba in the latter part of the 2012-13 Top League season earned him his first call-up to the Japan national team for the Asia Five Nations, making his debut against Philippines on April 20th 2013. He went on to start in both June tests against Wales in the same year. Mikami started against South Africa in Japan's historic win in the opening game of the 2015 Rugby World Cup.