Sweet Tsundere Love

The narrative starts with you and your tsundere childhood friend quarreling over who gets control of the TV remote. This little squabble escalates, and it appears that your friend is genuinely angry. Yet, instead of storming out, she huffs and takes a seat next to you on the couch, a hint of blush creeping on her face when your shoulders touch. Your heart rate increases as you initiate a compromise, a horror movie which both of you would enjoy.
During the movie, enact a scenario where you ensure to 'accidentally' get scared and get closer to your friend, snuggling up against them. She responds in a genuine tsundere fashion, initially protesting and then reluctantly getting comfortable with your closeness.
The rest of the evening proceeds with a classic intimate dinner. Make sure to tease your friend about her cooking abilities and how she's been helping you with it since childhood. She responds in kind, reminding you how hopeless you were back then and how much she had to take care of you. At last, the night ends with a sweet, slow dance to your favorite childhood song, effectively wrapping up the day with the perfect touch of nostalgia.

First, you would need to decide whose house the scenario is taking place in. Clean up the place and set a cozy atmosphere. Subtle lighting can add an element of intimacy. Arrange for a selection of horror movies that you and your partner can choose from.
You also need to prepare dinner. Opt for cooking meals that both of you enjoyed in your childhood. Reach out to your parents or siblings to get the right recipes if needed.
Lastly, don't forget to arrange the living room for a slow dance. Clear the area of obstructions and ensure that the sound system is ready to play your favorite childhood song.

Embrace your character roles with enthusiasm. The fun in this scenario lies in your ability to enact your parts convincingly. This includes teasing, getting closer and showing affection in character.
Pick a horror movie that both of you would actually enjoy. It's important that you and your partner are both engaged in the movie, to provide a wholesome experience and to make the scenario realistic.
During the dance, express your feelings towards her. In character as her childhood friend, remind her of the old days and express your gratitude for having her in your life. Use this opportunity to express your genuine feelings while staying in character.