HANA and NI were siblings. HANA had thingies of an adult nature but his sister NI didn’t. To keep herself amused she was fond of pole-dancing around a tree. One day naughty brother HANA hid a sharp stone in the tree bark which caused a minor wound in an naughty place.
This unexpectedly led to sexual misbehavior. The resulting offspring were left to their own devices as HANA was taken into care by the authorities to become the Moon and NI had to set off to rise again as the Sun.