のどが渇く by Tsurezure-aki
Summary by platina:
Prologue: A sick little Marisa riding on her father's hat desperately begs for water. Father Marisa tells her to hang on, they'll reach water soon...
Flashback: A Chen bounces through the park, mindlessly announcing that she's happy because she found sweet-sweets. Marisa would like to let her little one eat human sweet-sweets, so almost without thinking, she attacks and kills Chen.
Little Marisa is unimaginably happy eating the sweet-sweets, and it makes Father Marisa just as happy to watch her. However, ten minutes later, little Marisa is groaning in discomfort and thirst. Marisa carries her to the pond.
However, in the past day, a wall has been erected in front of the pond. A crowd of thirsty yukkuris has gathered, fruitlessly hitting the wall or trying to dig under it.
A group of housewives arrive and start squashing the yukkuris--today is extermination day, and to make the job easier, they walled off the pond and set out poisoned food that would make the yukkuris thirsty.
Marisa flees from the carnage and takes her little one to the public restroom instead. Being a former pet yukkuri, Father Marisa knows what a human toilet is and finds it disgusting, but since it's a matter of life and death, she presses her face against the toilet rim and lowers her little one in to drink.
However, one of the housewives finds them and exclaims out loud how disgusting it is that filthy manjus are drinking from a public toilet. When little Marisa learns that she was drinking from and licking a toilet, she throws up her bean paste and dies. Another housewife pushes Marisa down into the toilet with a plunger and flushes until she melts and gets flushed away.