Kasumi is one of the main trio of Asobi Asobase. Along with Olivia and Hanako, she makes up the Pastimers Club. Kasumi is mostly depicted as a quiet and shy person, but possesses a scary personality when she becomes serious — especially when it comes to competing or playing games. She has a secret hobby of writing BL fanfiction and playing BL games with dwarf x goblin pairings.

Kasumi has a complicated relationship with Tsugumi, and bringing up Tsugumi at all will cause Kasumi to blush and babble. Tsugumi seems to regard Kasumi with mild interest and amusement, especially when she gets so flustered.