Kaito, initially skeptical and resistant, quickly realizes that Luna can phase through walls, float, and emits a pheromone-like aura that lowers inhibitions. After a comedic but forceful encounter (where Luna uses her powers to immobilize Kaito), they end up having sex. Post-coitus, Luna regains a fragment of her memory: she is one of three “sisters” who fell from the “Second Floor” — a term that refers to a parallel dimension overlapping the apartment building. A few days later, another girl crashes through Kaito’s ceiling — this time from the actual second floor apartment. Her name is Mitsuki , a quiet, dark-haired human girl who lived above Kaito. She reveals that after Luna’s arrival, the dimensional barrier weakened, causing a “fusion” phenomenon. Mitsuki has partially merged with a parasitic energy entity, giving her tentacle-like hair extensions and a split personality.
The girl introduces herself as , claiming to be a “fallen celestial being” — a type of amnesiac spirit from another dimension. She has no memory of her past, only that she needs to absorb “life energy” (seinen energy) to survive in the human world. The only way to transfer this energy is through physical intimacy. Joshiochi-- 2-kai kara Onnanoko ga... Futtekita-
Unlike Luna’s playful, dominant nature, Mitsuki is shy and apologetic, but the parasite inside her forces aggressive sexual behavior. Kaito must now “stabilize” both Luna and Mitsuki by regularly transferring energy. The episode ends with Luna revealing that a third sister will fall soon — and that all three must “resonate” to prevent the building from collapsing into the void. A few days later, another girl crashes through