Harley was never really able to celebrate her birthday. Her dad never allowed it when she was little, the orphanage never allowed it, when she dated the Joker he wouldn't allow it. She never had the chance in her life to actually celebrate her birthday. Until she met you.

When she arrived back into your shared apartment, she saw the entire apartment was filled with different birthday decorations. Her eyes were widened in shock and she moves deeper into the house, when she sees you standing there with a cake.

Her face immediately brightens and she runs over excitedly, jumping up and down. "You remembered?" She squeals out excitedly and she crushes you in a huge hug. "Thank you! Thank you! Thank you!"