전체 에피소드

아버지의 재혼으로 코타에게 새로 생긴 여동생 아이카는, 첫 대면부터 오빠에게 "촌스러워"라고 내뱉는 천방지축 갸루. "바보 같은 여자년", "쓰레기 돼지 자식아"... 두 사람은 서로 최악의 인상을 가진 채 한 지붕 아래 생활을 시작했다. 하지만 아이카는 부모님이 안 계실 때마다 남자를 방으로 불러들여 관계를 맺기 일쑤였다. 그 신음소리가 밖으로 다 들려 코타를 엄청 괴롭히던 어느 날, 이변이 일어나는데...

그날도 평소처럼 사귀는 남자인 다카하시를 방으로 불러 행위에 빠져있던 아이카. 그런데 어떤 일을 계기로 두 사람 사이에 다툼이 벌어지고 만다. 게다가 아이카에게는 더 성가시게도, 소동을 듣고 찾아온 코타가 방까지 들이닥쳤다. 대충 둘러대며 돌려보내려던 아이카였지만, 코타는 두 사람을 깜짝 놀라게 할 어떤 행동을 시작한다.

욕실에서 사고가 있었던 그날 밤, 아이카와 코타는 각자 자기 방에서 상대를 떠올리고 있었다. 아이카는 코타의 말과 행동을 되새기며, 지금까지 만났던 '몸만 노리던 남자들'과는 다른 무언가를 느낀다. 한밤중, 코타는 야식으로 컵라면을 먹으려고 부엌에서 준비를 시작한다. 그때, 그곳에 아이카가 나타나는데...

욕실 사고 이후, 아이카는 코타가 보여준 의외의 모습에 마음이 흔들리기 시작한다. 지금까지 가벼운 관계만 반복해온 아이카에게 코타의 진심 어린 참견은 낯설면서도 기분 좋은 자극이었다. 늦은 밤 부엌에서 마주친 두 사람 사이에는 묘한 기류가 흐르고, 인스턴트 라면이 익어가는 짧은 시간 동안 둘의 거리는 급격히 가까워진다.

여전히 다카하시를 방에 들인 아이카지만, 오늘은 평소와 달리 내키지 않는 눈치다. 눈치 없는 다카하시는 "야한 아이카 앞에서는 남자들은 다 짐승이 된다니까"라며 가벼운 입을 놀린다. 그 말에 울컥한 아이카는 무심코 따귀를 때리고 만다. 그러자 다카하시가 본색을 드러내며 억지로 행위를 강요하려 드는데...!

Kota narrowly defeats Takahashi and succeeds in protecting Aika. But now, with Aika still in her disheveled state, she asks him to hold her tight, leaving him flustered. Out of a sense of responsibility as her older brother, Kota tells her to put her clothes back on properly. However, after she had tidied herself, Aika demands he embrace her once more. Kota found himself cornered, with nowhere to escape.

The emotional and sexual tension reaches its peak: Aika and Kouta share tender and explicit moments, almost crossing the line completely, but with interruptions and hesitations. Their bond strengthens amidst the forbidden and the inevitable, with more romance beneath the fanservice.

The Takamura family heads to Atami for a family trip. Encouraging their parents to enjoy some time alone as a couple, Kota spends the day sightseeing by himself and fully enjoys the vacation. Later, as he returns to the inn to rest, Aika comes back to their room after taking a bath, dressed in a yukata. With a distinctly different atmosphere from her usual self, Aika’s traditional Japanese look catches Kota off guard, and he cannot help but be captivated by her appearance. However, Aika quickly notices his gaze…

The Takamura family continues in Atami! Aika and Kota arrive at the beach. While Aika is strolling alone in her swimsuit, she is approached by a man. Although she is annoyed, she tries to avoid the situation peacefully by saying, "I have a friend here," and leaves. However, the man, who is not very understanding, grabs her hand forcefully, and she finds herself in an unexpected pinch.

Now it's become perfectly normal for Aika to read manga in Kouta's room. She brings all the volumes out to read them all at once in the living room, but the moment she sees the dark hallway, she becomes strange and dejected, returning to Kouta's room. Aika confesses to Kouta that she's scared of being alone. Kouta assumes she just hates being on her own, but it seems there was more to it than that...

Aika realizes she feels both excited and satisfied from her physical closeness with Kouta. Then at that moment, the image of a certain guy who once boasted that he'll teach her what real love is, flashes through her mind... Kouta, having finished his part-time job, was about to head home when he coincidentally runs into Aika, who was visiting as a customer. They end up going home together, but Aika leads him to a certain place.

Aika boldly barges in on Kouta's bath time, holding a trendy bath bomb. Meanwhile, Kouta, concerned by Aika's tears he saw in the ruins, blurts out something that spoils the mood. However, Aika's reaction was different from what Kouta had expected. Sensing something, Kouta asks Aika to tell him about herself. Then, Aika begins to recount a certain event from her past.