That year, Mizuno was put in charge of writing the song 'Yell' as the set piece for the junior high division of the 76th annual NHK Nationwide School Music Contest. On March 4, 2009, their first-ever collection of video works, 'Tottemo Ēzō', was released. On December 31, they debuted in the 59th NHK Kōhaku Uta Gassen festival. This album topped the Oricon weekly charts, becoming their first work to achieve a first ranking on any chart. On December 24, they released their third studio album, My Song Your Song. On July 7, they came out with their tenth single, 'Bluebird', which also became an opening song for the Naruto anime, and the group's first to crack the Top 3 in Oricon Singles. This album's live tour was from March 30 to May 23. Their second major studio album, Life Album, came out on February 13, 2008, debuting at number 2 on the Oricon weekly album charts.

Between May 24 to June 14, they went on a live tour to support this album. They released their first full-length studio album on March 7, 2007, entitled Sakura Saku Machi Monogatari, debuting at number 4 on the Oricon weekly album charts. Between November 10 and November 30, they held their first live tour, called 'Ikimonogakari no Minna-san, Konni-Tour! 2006'. Their second single 'Hanabi' was released on May 31, 2006, earning the band their first appearance on the Oricon top 10 chart with a number 5 debut. This was their major label debut with Epic Records Japan of Sony. On March 15, 2006, the band released their first single, SAKURA, produced by Masanori Shimada. As they were then performing with three members, the band did a cover of Yuzu's single, 'Natsuiro' ( 夏色 'The Colors of Summer'). Yoshioka was the younger sister of one of their classmates she entered as the main singer and the band took on its present-day form.

In those days, Mizuno and Yamashita planned to make a group with a female lead vocalist, which would be an unusual sound for the street performances they were doing.

In November 3, 1999, Yoshioka joined the band. At first, they did covers of Masayoshi Yamazaki. Yamashita and Mizuno formed their band on February 1, 1999, and began performing live on the street not taking it too seriously, they named it 'ikimono-gakari' after their shared experience in first grade. Yamashita later noted that he really wanted to be a 'blackboard monitor'. In 1989, Mizuno and Yamashita met by chance while they were in the first grade they were both put in charge of being Ikimono-gakari ( いきものがかり), who are caretakers of the school's plants and animals.

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