Fucking finally! the whole point of him getting a job at fairy house was to get cake for his sister, it should not have taken 24 chapters for them to learn of her, I mean look at how cute she is, why is he hiding her?!
I guess it's just him being socially awkward makes it hard to talk about himself or his family. He probably just planned to buy the cake at the end of the day without raising a fuzz, but he got involved in all the drama.