He appeared in a number of Japanese TV dramas, including Mei-chan no Shitsuji, Hanazakari no Kimitachi e and Zettai Kareshi.
Mizushima first appeared on Japanese television in 2005, where he played Hiro Misawa, a minor character in the second season of Gokusen.
Later that year, Mizushima starred alongside Shun Oguri in the drama Tokyo Dogs, playing a detective who is a hot-blooded fighting expert due to his earlier days as a delinquent.
He also starred in the feature film Drop in the same year in the role of Tatsuya Iguchi, a middle school student in a delinquent gang.
In 2010, Mizushima landed the role of Ryusuke Minami in the film Beck, in which once again acted alongside Mei-chan no Shitsuji co-star Takeru Satoh.
[6] In August 2015, Mizushima announced that he would appear as a guest cast in the fifth season of HBO's Girls, which aired in 2016.
[7] On January 14, 2020, Hiro was announced as an ambassador of the upcoming eight installment of Shimajiro 3D CGI animated movie, which was released on February 28, 2020.
One of the aired episode also guest starring his fellow actor from Kamen Rider Kabuto, Yūki Sato.