As a junior athlete, Tanno won two silver medals at the Asian Junior Athletics Championships, setting a national record in 2004, and she also reached the final of the World Junior Championships. She competed at her first World Championships the following year and won two bronze medals at the Asian Championships. In the 2006 and 2007 seasons, she won bronze at the 2006 Asian Games and two silver medals at the Asian Championships. She also helped set a new national relay record and became Japan's first ever female sprint semi-finalist at the 2007 World Championships. She was less successful at the 2008 Beijing Olympics and 2009 World Championships as she was eliminated in the heats at both events.