Tanaka was not seen as one of the top prospects in Japan whilst at University, but after joining the Panasonic Wild Knights in 2007 he played alongside former All Blacks fly half Tony Brown who was credited with helping him to develop immensely and Tanaka himself cites Brown as one of the most important influences on his career.

[5][6] After performing well at the World Cup despite it being a disappointing tournament for Japan, along with hooker Shota Horie he was signed by Otago and reunited with Tony Brown, his former teammate at the Panasonic Wild Knights who was now his coach.

[9][10] Following his good performances with Otago, he became the first ethnic Japanese player to sign a Super Rugby contract when he was named in the Highlanders squad for the 2013 season.

[12][13][14][15] After initially being limited to mainly to substitute appearances behind All Blacks scrum half Aaron Smith, in Tanaka's second start in Super Rugby he was highly lauded for his performance against the Blues which even drew positive comments from the IRB CEO Brett Gosper.

[16][17][18][19] In June 2013, Tanaka helped inspire Japan to their first ever win over Wales where he continued his run of form and was praised as one of the game's outstanding performers.