Cousin/friend knees me

This story is a couple of years old, hence I might not remember the exact details. Also english is not my native language so I apologize for any grammatical errors. All characters are 18+

I was born in grenoble but since I was born, my family moved to Nantes where I spent most of my life. However, we had to move back to grenoble after a lot of years, leaving behind all the friends I made there. Back in grenoble, I didn't know anyone. My dad had a close friend living there though, from whose help we could find a place to live and other basic stuff. He had two daughters, Olivia and Emily. Olivia was a tall, fit, healthy and a strong girl, even taller than me, and is around 3 years older than me, while emily is 4 years younger than me. We hung out a lot, and spent a lot of time together. We eventually became good friends and our parents were already pretty close.

One day, Olivia and I were alone at their house. Our parents along with Emily had gone out. Olivia was wearing a short black dress, which was above knee length, and I was in grey sweatpants and a black sweatshirt. Olivia and I were chilling, watching TV, and talking about random stuff. This is when she told me her dad enrolled her for self defence classes because of the increasing crime in grenoble. I told her that's nice and everyone should be taking these classes for the worst case scenarios. She asks if we could do a play fight because she wanted to show me what she learnt. I agreed. She told me the rules, basically we won't hit each other, but would just throw punches or kicks that stop mid air.

So we started the fight. She was strong and I could feel her strength when she used to grab or defend my hits. The fight went on for maybe a minute or two and I proceeded to kick her on the side of the ribs with my right leg. The kick was quick but surprisingly she held my leg. Here I was, waiting for her to do the next move. She then proceeded to lift her right knee and almost hit me in the balls. She did that once, then lowered her knee, and lifted it again, bringing it closer to my body than before. For the third time, she lowered her leg, and powerfully rammed her knee into my balls. My body couldn't take it, and my reflexes made me get my leg out of her grip and I fell to the floor immediately clutching my balls.

For me everything went blank. The pain shot up so bad that I didn't understand what was happening. All I knew I was in pain, rolling on the floor, groaning 'my balls my balls'. At first Olivia started laughing at whatever was happening. But after a couple of minutes when i was still on the ground, and still in pain holding my balls, she knew she messed up. She now started to become concerned for me. She sat on her knees next to me and was comforting me, asking if i was okay and if i needed anything, and was constantly apologizing. None of that made sense to me as i had no idea what was going around me. I was eventually able to stand up with her help, and she helped me walk to the couch where I sat down, still in pain but much better. I asked her obviously why she did this. The only thing she said was because she had seen this happen in movies and wanted to know if it really hurts this bad.

She kept apologizing for whatever happened. Fast forward to now. She's never hit me again but She keeps bringing up the topic since. mocks me saying the knee wasn't even that hard, and how I went down the moment she hit me and stuff. There are also some incidents where we disagreed with something and she proceeds to threaten me saying 'oh did you forget what happened the last time we fought' or like 'i miss the face you made when I hit you. Looks like I need to do it again'. One particular time I remember we were hanging out by the river, me Olivia and Emily. When I teased Olivia about something I don't remember, but she lifted her foot and made a fake kick towards my balls and said 'I'll kick you just like this'. To which Emily laughed. I find it tough to imagine what would have happened to me if the kick had connected...