1. Yu Ling entered the palace, which triggered the contraceptive story in the morning.
2. Entering Yangxintang in the middle of the night (there is no light in the big picture) has a chance to trigger.
3. after triggering 2, select "which family are you from" (politics > 200 triggers this option)
4. After Trigger 3, let Firefly wait in hall of mental cultivation until she gets pregnant and enters the palace (I don't know if it depends on her face for 57 times).