Diary of a Void by Emi Yagi

Ms Shibata refuses to clear away the coffee at work one day, because she's pregnant and can't bear the smell.

The only thing is . . .

Ms Shibata is not pregnant. Being a mother-to-be isn't easy. Ms Shibata has a nine-month ruse to keep up.

Before long, it becomes all-absorbing, and with the help of towel-stuffed shirts and a diary app that tracks every stage of her 'pregnancy', the boundary between her lie and her life begins to dissolve.