Yajima was born in Saitama on January 18, 1994. He joined J1 League club Urawa Reds from their youth team in 2011. However he could not play many matches. In 2015, he moved to J2 League club Fagiano Okayama on loan. He played many matches as defensive midfielder in 2 seasons. In 2017, he returned to Urawa. In 2018, he moved to Gamba Osaka. However there were few opportunities to play. In June 2018, he moved to Vegalta Sendai. In 2019, he returned to Gamba.