The artist posted the image with only the following relevant text: 「ウォシュレットで何かに開眼するあずにゃんちゃん」
"Azy-nyan-chan is awakened to something by the washlet."
The bidet function is by far the most likely explanation with the only remaining speculation being what kind of stimulation resulted (anal, clitoral, etc.). Some washlets have further functionality in terms of drying (blowing cool or hot air) and seat warming, among others.
