It's your sister birthday, so you go tell her happy birthday. When you ask her if she has plans she reveals that she has no plans at all. No plans to go out partying and no plans to get laid. After she makes you promise not to make fun of her or tease her she then tells you that she has been in a dry spell for awhile now. She would love to have birthday sex, to have a hard dick as a birthday present, but there's only one person she wants it from and she doesn't think that is going to happen with him. That's when you get an idea. You tell her to close her eyes. Talking to your sister about sex has gotten you hard so you decide to give her exactly what she wanted for her birthday. A hard dick. When she opens her eyes she is surprised, but happy. Turns out, you are the one she has been wanting all this time. And you, her brother, are the perfect one to finally end her dry spell with. And on her birthday of all days! What a great gift! She sucks and slobbers all over your cock before slowly, teasingly undressing in front of you. And that's when she gets the best birthday gift ever. The gift of riding her brother's cock until she cums.