Big-sis Marisa and Shelly lives under the tyranny of their mother Deibu and their shithead siblings Big-sis Reimu and Wasa who's been terrorizing them ever since their daddy passed away. Big-sis Marisa's only solace Alice, their neighbor who harbors affection towards Big-sis Marisa. Later it's revealed that Big-sis Reimu's shitheadedness came from an inferiority complex against Big-sis Marisa's natural talents and also jealousy over Alice's affection. Big-sis Reimu eventually had a change of heart and took to the two marisas side which unfortunately lead to her also being the subject of abuse by Deibu and Wasa.
Things took a turn for the worse when Wasa accidentally killed Big-sis Marisa out of anger. And it gets even worse when Deibu remarried with a Shithead Marisa. Shithead Marisa uses her strength to take over the clan and killed the other clan members for fun. Shithead Marisa even raped Alice which, along with the loss of her beloved Big-sis Marisa, lead to her suicide. Big-sis Reimu is helpless to stop Shithead Marisa's opression.
Shelly realizes that she and Big-sis Reimu won't survive much longer under the tyranny of Shithead Marisa and Deibu. Shelly recalls Big-sis Marisa's words, most humans are far stronger than yukkuris. She and Big-sis Reimu decided to venture out to find humans as a final gambit, hoping to encounter a kind human to help them but aknowledging that there's a good chance that they'll just be instantly killed. Seems like luck is finally on their side, they both encountered nice humans and got adopted as pets.
On the other hand, Shithead Marisa's overconfidence lead to her finally seek out humans to extort food and sweets. Karma hit them like a truck as they encounter abyusers who abuses them for fun, just like what they did to the other members of the clan. And the abyusers even used the same tricks and excuses the shithead family used themselves back when they abused other yukkuris (e.g. when Marisa killed Chen she said she doesn't care about the dying words of a weakling, and now as she's dying the abyusers doesn't care about her cries).
