In your honour, here's a very small ficlet I've made up on the spot. Hope your special day is wonderful.
With much love,
Hermione Granger yawned and opened her eyes slowly. Today was the 19th of September, which meant she was now sweet sixteen. She sat up and stretched, wondering what the day would bring. She didn't expect either Ron or Harry to remember her birthday; while they were her best friends, they were boys, and boys were not terribly good at remembering things like birthdays.
Her gaze fell upon the end of her bed and she was most surprised to find there was a solitary pink tulip resting on the cover by her feet. She scooted down to pick it up, but there was no note attached. Pink was her favourite colour and tulips her favourite flower, so whoever left it there had to know her.
Hermione's heart began to thump loudly. Could Harry had left it there? For quite some time, she'd noticed the subtle shift in their relationship. Hermione found herself wanting to spend more time with him and while she'd always loved him as a friend, lately she'd wondered if perhaps that love hadn't become something different. She could spend hours just looking at him, the way his hair fell around his face messily, the way he continually pushed his glasses up from sliding down his nose, and the way his green eyes seemed to be trained on her every time she looked at him.
Humming to herself happily, she accepted birthday wishes from Parvati and Lavender and then showered and dressed. Brushing her hair, she carefully cut the stem of the tulip and placed it in her hair, just above her ear.
When she went downstairs to the Common Room, she found both best friends waiting for her.
"Happy Birthday, Hermione!" Ron said, sweeping her into an enthusiastic hug. She hugged him back, grinning. "We have a present for you but you have to wait until tonight."
As soon as he'd let her go, she was in another pair of arms, and these arms were warm and strong around her and she didn't want Harry to move them again. Hermione curled her arms around his neck and hugged him tightly. She moved her lips to his ear and whispered, "Did you leave the tulip?"
She felt Harry nod. "I know they're your favourite."
"Thank you," she said, pulling back far enough to look at him. The smile on his face was contagious, and she couldn't help but smile back.
"Close your eyes," he said softly, seemingly unconcerned about their audience. She did was she was told, and almost melted on the spot when his lips pressed against hers gently for a few moments. "Happy Birthday, Hermione," he whispered against her lips.
Somehow, Hermione Granger thought that this might just be the happiest birthday ever.