Her career as a musician began with her performance of the opening and ending themes of the anime series K-On!

In the same month, she and three other voice actresses debuted as the musical group Sphere with their single "Future Stream".

and held the leading role in K-On!, providing the voice of protagonist Yui Hirasawa.

[16] In 2014, she voiced Seitenshi in Black Bullet,[17] and was the third gender main character Izana Shinatose in Knights of Sidonia,[18] which was also broadcast as a Netflix-exclusive series.

[21] She, Ayahi Takagaki, Haruka Tomatsu, and Minako Kotobuki appeared twice on the Anime Song Plus (アニソンぷらす, Anison Purasu) television show as the musical group Sphere on 20 April 2009, and 27 July 2009.

[23] At the 2010 Seiyu Awards, she was named as a "Best New Actress" for her role as Yui Hirasawa and Kana Nakamachi.

[25] In Animage's annual Anime Grand Prix awards, Toyosaki placed first overall for Best Voice Actor in 2009.

Girls" and "Don't say 'lazy'", respectively, with voice actresses Yōko Hikasa, Satomi Satō, and Minako Kotobuki.

[31] The opening and ending singles remained on the chart during the week of 27 April to 3 May, falling to sixth and fifth, while selling an additional 19,963 and 22,094 copies.

[33] Toyosaki then performed the opening theme of the 2009 First Love Limited series, titled "Future Stream" with Ayahi Takagaki, Haruka Tomatsu, and Minako Kotobuki.

[37] Shortly after, Toyosaki, Kaoru Mizuhara, and Rie Kugimiya performed "Heart Connected to You", the opening theme of Kanamemo, which was released 5 August 2009.

[38] On 25 June 2009, she provided the narration of a television advertisement for the performance of "Blue Feather", a single by the musical group Binecks.

[24][42] The mini-album sold over 67,000 copies to debut at the number one spot on Oricon's latest weekly album chart.

[46] After, the group performed the opening theme of Ichiban Ushiro no Daimaō, "REALOVE:REALIFE", which began airing in April 2010.

[48] Sphere next performed on the first day of Animelo Summer Live 2010, at Saitama Super Arena on 28 August 2010.

[51] In October, the Otome Yōkai Zakuro anime premiered with Sphere's "MOON SIGNAL" as the opening theme.