Flan was being abused by a human, but was saved by the intrusion of police. She escapes into the forest, where Dosu finds her and treats her back to health despite some initial distrust. Dosu tells Flan that she can tell if a yukkuri is easy, and as Dosu, it's her duty to let easy yukkuris take it easy, which was why she saved Flan.
Dosu later brings Flan into her clan, and after some initial fear, they vote to let Flan in. Flan proves to be extremely useful in many ways, but the clan actually makes use of her. They bully her after everyone returns home, taking her food and pooping in her nest, threatening to tell Dosu that Flan was bullying them if she fought back. Flan simply bears with it, always acting normal in front of Dosu.
One day, Flan vanishes. Dosu notices, and immediately asks for the truth. The rest of the clan, led by a Marisa, say that Flan was uneasy, which was why they punished her every night. Dosu is shocked, but asks everyone to go find Flan. However, they refuse, and Marisa leads an uprising, torturing and killing Dosu despite her pleas for them to stop.
Elsewhere, Flan is living day by day apart from other yukkuris. One day, she hears some yukkuri talking about a clan with a kind Dosu, but with the rest of the clan being scum. Fearing the worst, Flan interrogates them, and finds out which direction that clan is in: In that direction... lies Dosu's clan only. When she releases her hostage, they gather to punish her, but the look of rage in Flan's eyes makes them faint dead away...
Back at the clan, Marisa is celebrating her new position as the clan leader, and decides to send everyone out to look for Flan, since Flan is such a useful slave. But Flan is already there, in shock at what happened to Dosu. She then snaps when they make rude demands of her, slaying an Alice.
They say that they'll tell Dosu, but Flan just chuckes...
"That Dosu, didn't you all kill her already...?"
The yukkuris panic when they realize that they've thrown away their only chance of controlling Flan, and Flan begins the mass extermination.
She first stabs the Marisa, the leader of everything the clan did to her and Dosu, putting her up so she can watch the entire thing. Flan then taunts them, saying she couldn't have won against Dosu. The yukkuris, encouraged by the fact that all of them working together beat and killed Dosu, gather to punish Flan.
When Flan sees that they've all gathered like she planned, she proceeds to kill them one by one, not eating them, but discarding everything she rips away. Myon, Alice, Chen, Reimu, one by one, all the yukkuris in Marisa's clan are slaughtered in front of her eyes, until only three are left. Marisa, Flan and...
Yuyaaaaaaan! Pyapyaa! Hwelllppp!”
The head Marisa's child was a red Marisa. Right now it was inside Flan's mouth, wriggling and squirming in a way that seemed miserable.
“S-stop it-ze! Let go of the little one! You trash!”
“You...when Dosu told you to stop, did you...? Ahaha, hahahahaha!”
“Don't know anything about that small fry -ze! Don't compare little one to that -ze!”
“Ahahahaha! So it was as I thought? Then...I won't stop either!”
“Yunyaaaaaa! Id hurrddzz!”
So that it could watch the red marisa's last moments in the darkness, the chief marisa approached flan with all of its might. Flan's mouth began to close, little by little over a long period of time.
“Pyapyaa! Dun wanch chu dwiee!”
“S-stop it pleeeeaaasssseeee! It was Marisa's faulltt! Marisa will become Miss Flan's salve!!”
“Heee~ A slave huh~?”
“”T-That;s riiiight! So save little oneeeee!”
Then Flan had an idea. With a smile plastered across her whole face
Flan closed her mouth with all her strength, smashed the final words of the Red Marisa.
Marisa rages at Flan for eating her little one, but Flan laughs and spits out the remains, saying she won't eat something so disgusting. She finally begins killing Marisa, ripping off piece by piece and discarding it, ignoring any pleas or apologies, since they've come too late.
Her vengeance complete, Flan goes over to the corpse of Dosu, crying more than she did when Dosu offered her kindness long ago. She bids Dosu farewell, flying up high as though saying 'it's thanks to Dosu Flan is this energetic', turning those crimson eyes outwards and away.
"Good night... Dosu"