anko3771: Aquatic Conquerors
Summary by platina:
Some upper-elementary boys are playing by the river, floating pieces of rubbish downstream and throwing rocks at them. To make his friends laugh, one boy tries to stand on a big floating plank and pratfalls into the water. However, he's annoyed when a nearby group of Aquatic Marisas (one adult and a bunch of children and babies) also laugh at him and mock him for being unable to float the way they can.
The boys start throwing rocks at them. The little Marisas are flustered by the waves, and one Komarisa is clipped and falls into the water in pain, but for the most part, they're too small for the boys to easily hit. They focus their barrage on the big Marisa, who is trying to rescue the one who fell in. Rocks bounce off her and hit the water all around her, and finally a rock directly hits the drowning Komarisa, killing her and sinking her. Big Marisa tells the other little ones to flee towards the opposite shore. Another well-placed rock takes out another Komarisa.
Big Marisa sends the little ones ahead of her and hangs back to act as a shield. The boys are momentarily impressed by the nobility of her self-sacrifice, but then decide that since she seems to be their parent or teacher, this is all her fault for encouraging the little ones to laugh at the humans. In actuality, Big Marisa is both teacher and parent--a few of the little ones are her own, and the others are friends and neighbors' children who she was helping to practice floating. She is filled with remorse for the whole incident, and she expects that she will be punished for letting two of the little ones get killed.
One boy who plays baseball manages to sink a sharp-pointed rock into Marisa. The other boys pelt her with rocks. Badly wounded, she tells her little ones to look after their mother and sisters. Since he's already wet, the boy who fell in the water wades out after her and, waving the big plank, knocks helpless Marisa into the water where she dies.
Since the remaining Komarisas are so tiny and far away, the boys have stopped throwing rocks at them and are thinking of going home. However, the overconfident little ones, believing that they're safe, start taunting the boys. Newly motivated by the yukkuris' genius for annoying humans, the boys head for the nearby bridge.
Reaching the opposite riverbank, the surviving little ones tell their parents what happened. The adult yukkuris swear they'll punish those scummy humans, but just then, the boys arrive in their midst, saying, "Well? Go ahead and try punishing us." The yukkuris are frightened, but goaded by the boys, they make a futile attempt at punishing them.
One boy kills an adult Marisa for her hat, fills the hat with little Reimus, and sets it afloat. Saying he'll help their mother Reimu save them, he flings Reimu at the hat. Fortunately (and to the boy's surprise), she lands right on top of the hat. Unfortunately, there's a hole in the tip of the hat, and it's rapidly filling with water. Reimu manages to get the little ones into her mouth, but in the end, she sinks along with the hat, and the little ones cower in terror inside her at the bottom of the river until her body dissolves and the water gets them too.
The boys kill the yukkuris until only the little Aquatic Marisas are left. The boys say it's all their fault for insulting humans, and the terrified Komarisas argue that that doesn't justify killing the entire clan. The boys admit that maybe they overdid it a little, but there's nothing to be done about that now. Of course, they'll still kill the little Marisas. They repeat that yukkuris have some kind of genius for annoying humans.
The boys take two Marisas' hats and make them gouge their own sisters' eyes out to get them back. They yell "Shotgun!" and pelt them with gravel. They force them to eat pebbles and float them on their hats to slowly sink under the weight of the pebbles.
When all the yukkuris are dead, the boys head home, making plans to find more yukkuris and do this again tomorrow. In the end, they did this all for fun.