Koike made her acting debut in the Japanese television drama Botan to Bara as Rika Nojima in 2004.
2007 was also the year Koike made her first appearance in films starring in Sakuran[1] and Always Zoku Sanchōme no Yūhi.
[2][3] In Sakuran, Koike played the part of the young Kiyoha, the main character of the story.
[3] In 2010, Koike played Mizuki Tsuji in the stage production Alice in Deadly School.
[4] In 2011, Koike was starring in Into the White Night, the theatrical adaptation of Journey Under the Midnight Sun.