[1][2] She is best known for playing lead roles in Ouran High School Host Club (2012), POV: Norowareta Film (2012), Zekkyō Gakkyū (2013), Say "I Love You" (2014), and One Week Friends (2017).

After joining the child division of Ken-On, she made her debut in the October 2007 issue of Nicola released on September 1 of that year.

On July 9, 2009, she made her first appearance in a music video with Shunsuke Nakamura for Hi-Fi Camp "Dakara Ippo Mae e Fumidashite" which was used as the commercial song for Pocari Sweat "Unmei no Natsu-hen (Summer Edition of Fate)".

In early August, she toured 12 cities across Japan at the event "Pocari Sweat o Nonde Kawaguchi Haruna・Hi-Fi Camp ni Aou!

In November 2011, she became the seventh support manager (image girl) for the 90th National High School Soccer Championship.

[11] In 2013, she starred in the movie adaptation of "Real Escape Game" which was also made into a drama Madam Marmalade no Ijō na Nazo.

It was released as a mystery solving movie with audience participation called "Nazoto Kinema" which was divided into "questions" (October 25) and "answers" (November 22).

[12] In 2020, she played Kicho (Nohime) in the NHK Taiga drama "Awaiting Kirin" due to the previous actress, Erika Sawajiri, dropping out due to being arrest on suspicion of violating the Narcotics Control Law before the start of broadcasting.

[20] On December 31, 2021, she was one of the hosts for the 72nd NHK Kōhaku Uta Gassen with Yo Oizumi and Mayuko Wakuda.

From the first to third year of junior high school, when going to work, there was no direct flight to Tokyo, so she traveled to and from Hakata by boat for nine hours.

[30] She is also good friends with Riisa Naka, her costar in Yankee-kun to Megane-chan, who is also from Nagasaki Prefecture.

[33] When she appeared in Aitsu Ima Nanishiteru?, according to her classmates from elementary school, Kawaguchi was more funny than cute at the time; she imitated Takayuki Haranishi of FUJIWARA so she was never popular.