Her roles include leads such as Ryuko Matoi in Kill la Kill, Charlotte E. Yeager in Strike Witches series, Kallen Stadtfeld in Code Geass, Anemone in Eureka Seven, Irina Tachibana in Rio: Rainbow Gate, Nadja Applefield in Ashita no Nadja, Leonmitchelli Galette Des Rois in Dog Days, Shizuri Mugino in A Certain Scientific Railgun series, Yumi Hoshino in KimiKiss: Pure Rouge, Takuto Hasegawa in Magician's Academy, Hibiki Hojo in Suite PreCure, Nanaka Yatsushiro in Myself ; Yourself, Ersha in Cross Ange, Himari Noihara in Omamori Himari, Sailor Jupiter in Sailor Moon Crystal, Mikumo Guynemer in Macross Delta, Nodoka Haramura in Saki, Tenma Tsukamoto in School Rumble, Holo in Spice and Wolf, and Yang Xiao Long in both RWBY (Japanese dub) and RWBY: Ice Queendom.

In video games, she voiced notable characters like Agnès Oblige in Bravely Default, Mai Shiranui since KOF Sky Stage, Mist in Rune Factory, Rimurisu in Tears to Tiara, Rinka in the Atelier series, Miyabi in Zenless Zone Zero (Japanese Dub), Rosa Ushiromiya in Umineko: Golden Fantasia, Tsuruhime in Sengoku Basara, Yukiko Amagi in Persona 4, Captain/Major Claire Rieveldt and Musse Egret in The Legend of Heroes: Trails of Cold Steel series, Beidou (Hokuto in Japanese) in Genshin Impact (Japanese Dub), and Zima and Projekt Red in Arknights.

[5] In the second year of junior high school, she was over 160 cm tall and was troubled by the fact that she could not get roles as a child actor.

She continued her career with roles in School Rumble (as Tenma Tsukamoto), Onegai My Melody (as Miki Sakurazuka), and Eureka Seven (as Anemone).

[9] On September 30, 2011, Koshimizu left Production Baobab, where she had belonged for four years, and joined Axlone on October 1, 2011.