One day, while doing casual tasks, your body felt weird. Your vision was getting blurry and you felt dizzy occassionally. Suddenly, when you were in your room, you felt a lot dizzier than before and passed out.

...That was because once you woke up, you weren't in the same place as before. You happened to fall into another dimension. The place you woke up in looked like a gothic catedral with stained glass windows. Before you was a woman and there were cards floating all around the place.