1Migi y Dali
Los Sonoyama siempre quisieron tener un hijo, así que ya siendo muy mayores, deciden que es el momento de adoptar uno. Cuando llegan al orfanato buscando elegir al nuevo miembro de su familia conocen a un pequeño que enseguida les llega al corazón: Hitori. Lo que no saben es que este niño tiene cierto oscuro secreto.
2Welcome Party
Migi and Dali have been fully accepted as members of the Sonoyama family. They behave just like real parent and child, but the twins notice that Mom and Dad are acting somewhat distant. Suspecting that the Sonoyama couple might be hiding something, the two discreetly begin to search the house and stumble upon an unexpected secret of the couple. Migi and Dali are shocked, wondering if they have been deceived. However, determined not to let things end this way, they execute a plan to retaliate against the Sonoyamas.
3Let's make friends
To uncover the truth behind their mother's death, Migi and Dali finally begin to take serious action. Their clue is the memory of the room they lived in with their mother when they were young. They remember the dimly lit space under the bed and the wallpaper patterned wih daphnia. In order to locate the room, the twins come up with a plan to be invited over as friends to different houses. They promptly join the Boy Scouts to make friends, but the scouts offer their friendship on one condition.
4Be a good student
The housemaid Micchan tells Migi and Dali that the Ichijo family has a room with water flea wallpaper. They begin attending school to befriend Eiji, the son of the Ichijo family. However, to get close to Eiji, they need to score well on tests and join a top class. The two start studying diligently to boost their grades, but unexpectedly, Migi falls head over heels for a certain female student in the library.
5Water Flea's Song
After achieving first place in the test, the Sonoyama family was invited to the suspicious Ichijo residence. Dali, seeing this as an opportunity, thoroughly searches the Ichijo house. However, she falls into Eiji's trap, and Migi ends up being captured.
6Who Killed the Parent Bird?
Dali continues to search the Ichijo house. Migi, by perfectly playing the role of an infant, tries to draw out the secrets of the Ichijo family.
7It Wasn't a Ghost
"It was Eiji who killed our mother!?" To confirm the truth, Dali disguises herself as Sali and begins to approach Eiji alone.
8Two ≠ One
Shocked to discover that Sali's true identity was Dali, Migi flees to Akiyama's house to escape. Dali comes to bring Migi back for revenge, but Migi decides to live freely, not bound by revenge.
9Kill Kill Kill Kill Kill
Why did Eiji help him? To find out, Migi disguises herself as Sally and visits Eiji's house. Eiji shows Sally (Migi) around the attic and tells her about Reiko's and Eiji's secret, and how it has put Hitori in danger. However, Reiko has also seen them talking! Migi recoils from Reiko's strange aura. At that moment, Migi witnesses Reiko's terrifying true nature.
10Beavers vs Mother Ichijo
Framed as murderers by Reiko, Migi and Dali find themselves unable to reveal themselves and decide to seek help from Akiyama.
11Upside-Down Woman
Reiko, cornered by Migi and Dali, finally begins to speak about Metry, the mother of Migi and Dali. It turns out to be the story of their birth as well...
12Our Revenge
Migi and Dali, along with others, are trapped in a confinement room. Gradually, smoke from the fire started by Eiji begins to drift into the room.
13Migi and Dali
The Ichijo house was burned down, and the incident was resolved, gradually bringing life back to normal. Migi and Dali were supposed to return to their usual lives as well, but there was one difference.