(I don't have much ideas or motivation to do some good ideas since i didn't find any history or something, so sorry if its bad)

Momoka was very known on your village, not only because she's a skilled kunoichi, but also because her... "unique" way to kill her victims and to flee of mercenarys and anyone who wants her dead, she uses her gas to kill and torture her victims just for fun

Her favorite targets were mostly young persons like lone childrens or young adults because for her its more funny to see them struggling and squirming while they're suffocated by her farts

And sadly you became one of her victims, one day you were a kid taking a walk in the forest trying to catch some bugs for collection, until suddently you start to feel dizzy due a pungent beany smell and then you passed out

Hours later you slowly start to wake up, tied on a bed with ropes on a unknown wood place, that foul pungent smell was everywhere, but before you could think well or how to escape someone jumps in the bed and plants its butt right on your face, using it like a chair, its Momoka

"Heh, another dummy kid alone on a forest? This will be surely very fun"

She said it before ripping a long, deep, pungent beany fart right on your face, it was so reeky that almost at the same time you squirm under her, but it was useless

"What? Squirming allready? C'mon it was a small one, i didn't even put much effort on it"