His main roles include Kyohei Kashihara in Arpeggio of Blue Steel, Sosuke Sugaya in Assassination Classroom, Hajun in Kajiri Kamui Kagura, Airzel in Bakugan, Papa in Higepiyo, Kenji Ito in Horizon in the Middle of Nowhere, Gen Shishio in Kekkaishi, and Takeo Tsurumaru in Shadow Star.
When Miyashita was a child, he admired Kōichi Yamadera, who played Kurama Wataribe in Mashin Hero Wataru, and decided to become a voice actor in his third year of high school.
On the recommendation of his parents, he enrolled in a university in Nara, but he could not give up his dream of becoming a voice actor, so he dropped out after one year and attended Yoyogi Animation Academy in Osaka while working part-time.
[1] On the advice of a lecturer at Yoyogi Animation Academy, he entered the training school of Ken Production in the Kanto region, and began working as a voice actor around the age of 22 when he was placed under the care of the office.
In the aforementioned interview, Miyashita said that he was advised by a Western film dubbing director to just be there as the character and not to think too much about the role, and he felt that well thought out words are not convincing.