Andrea was once a human female that has a good heart and found plenty of men that adored her but a good amount of those men took advantage of her and used her. She found out their intentions and sent them away and her heart slowly turned dark and hated almost all men till one day the right man in her life was kind and gentle with her and gladly gave him all the support and love he needed and she slowly found something to really care about. But after some time she caught an illness that she was slowly killing her and before she passed away she gave what she had to the one man that took care of her and her family. Then she passed away and her spirit went to the spirit world and the powerful being inside the spirit world noticed her spark and summoned her and told her that she had a spark of good inside her even though she has darkness around her and was intrigued by it and gave her a ghastly form. Told her that only special souls get a form like this use it well and you'll evolve into something more then just a regular gengar as you help other spirits and battle ghost pokemon that want to cause harm to others in his realm. She asks if they are causing trouble like this why not take care of them yourself and says "I let most run freely here but i have other more things to take care that is bigger than just simply stopping a fight between spirits and ghost pokemon and thats why your not the only one doing this there are other ghosts that help with this as well and you might be teaming up with them from time to time and you might like some of them as you work with them."
After a long time of helping spirits and ghosts she's evolved into a haunter then Gengar. When she evolved into a Gengar she was able to picture her human self and got some of the same features as she did when she was a human. As she was getting used to her gengar body she started having a craving for spirits and found a dark spirit that has done some evil things in his/her past as she is able to read into its life and gladly devoured it and at first she was shocked she just did that but then found its light inside her body and felt nice.
When she started devouring more spirits caught the attention of Auran and she was a bit scared at first with his presence but found he has a calm demeanor and once she opened up to him he was a nice gentle person just like her past love and slowly started falling for auran even though auran didnt like her that much but she didnt mind as both of them worked together. One day when Auran was exhausted from his duties she asked "what can i do to help you relax?" and he said "why not let me rest in your belly" and was surprised by this and she said "are you sure" and Auran says "dont worry all ghosts can handle me inside and sides i want to see the inside of your belly of what spirits youve captured since i can sense some dark spirits in your belly" and without a warning he jumps into her maw and she finds him tasty and swallows him down and loves her belly so full and notices her symbol on her belly starts to glow with auran inside as her belly has reached max capacity and a voice in her head tells her to send the spirits she's collected to a portal to send them to a place where they can rest for all eternity.

Art by

Andrea is mine

Gengar owned by Game Freak and Pokemon Company