Iio has represented Japan at Under-20 level, but has yet to be given a full international cap. Iio was selected for the 2001 FIFA World Youth Championship, along with his strike partner at Verdy, Kazuki Hiramoto.
Iio made a name for himself when he scored Verdy's first goal in the final of the 2004 Emperor's Cup. The match ended in a 2-1 victory for Verdy over Júbilo Iwata. Hiramoto netted Verdy's second, whilst Norihiro Nishi provided Jubilo's consolation. It was the first time Verdy had won the Emperor's Cup since 1996.
Upon Iio's transfer to Avispa in 2006, he received a relatively high squad number of 34. Despite this, he quickly established himself as a first-choice striker. During the 2006 season, Avispa would usually play with two men up front, with Iio on the left, and Takanori Nunobe to his right.
Iio's first J. League appearance for Avispa came against F.C. Tokyo on 19 July 2006, when he came on as a 84th minute substitute for fellow striker Mitsunori Yabuta. This game was held at the Hakata no Mori Stadium, and ended in a goalless draw.
Iio would not have to wait long for his first Avispa goal however, as just 10 days later, on the 29 July 2006 contest between Gamba Osaka and Avispa, Iio netted a goal in a match that eventually ended in a 2-2 draw.
Following Avispa's relegation, Iio returned to Verdy for the start of the 2007 season. Iio would appear regularly for Verdy in this campaign, occiasionally even appearing as a right-winger in Verdy's midfield. He finished the campaign with 19 games under his belt, scoring 2 goals.