What gift should I give my sister for her birthday?

I think the cake is simple, but it is also a gift. If I were you, I would definitely give it, but I can add "Sister, I love you" or "I wish you happiness" when writing (this is what you want to say to your sister most). Since we are sisters, we have a good relationship and will leave soon. In order to miss each other, I will send one or more articles for daily use (such as bracelets and cups). If conditions permit, maybe I'll bring some small gifts to her daughter.

Personally, I think sometimes some vulgar ideas are the essence. The reason why it is "vulgar" shows that many people use it. Since there are many people using it, it means that many people have recognized it. You might as well try it.