Not long after having seen a 1997 Japanese film entitled Chikyuu ga Ugoita Hi ("The Day the Earth Moved"), all of these events inspired Kotobuki to pursue her career as a voice actress.

PreCure, Mitsuko Kongō in A Certain Magical Index and A Certain Scientific Railgun, Yūko Nishi in A Channel, Lana and Cia from Hyrule Warriors, Natsumi Aizawa in Natsuiro Kiseki, Touko Nanami in Bloom Into You, Asuka Tanaka in Hibike!

Kotobuki performed the opening and ending themes of the 2009 anime series K-On!, alongside Aki Toyosaki, Yōko Hikasa, Satomi Satō and Ayana Taketatsu.

[4] She performed the opening theme for Hatsukoi Limited series, with Aki Toyosaki, Ayahi Takagaki and Haruka Tomatsu.

She also played the keyboard on some of her own songs during her Our Stride solo concert tour and on Sphere's first 2013 live event, Music Rainbow 02.