My Blooming Sisters (花咲く妹たちHanasaku Imōto-tachi) is the 10th episode of the Kono Naka ni Hitori, Imouto ga Iru! anime series.
Synopsis
With the help of Yuzurina Houshou's influence, Shougo Mikadono invited to the Mikadono Group party Konoe Tsuruma, Miyabi Kannagi, Mei Sagara, Rinka Kunitachi, and Mana Tendou. Miyabi however acted differently during the party, and later on disappeared without a word.
While looking for her, Shougo and Ikusu Mizutani discovered that reveal that Risa Seri was taking via phone to someone who was conspiring with to remove Shougo's candidacy as the next head of the Mikadono Group by revealing the existence of Kumagoro Mikadono's illegitimate child. Ikusu advised Shougo to pretend being oblivious to the betrayal the time being, as he was unable to protect his little sister for now, while reassuring him that his mother was prepared to face competitors within the Mikadono Group.
Afterwards, Shougo revealed his discovery to Yuzurina, who just had found Miyabi in the hotel. While Yuzurina was dismayed about Seri's scheme, she was also fine with publicizing herself as Shogo's little sister. She also told Shougo to find a wife among his schoolmates as a way to cement his claim to the Mikadono Group, an advice which Shougo accepted wholeheartedly. Finally, they talked about Miyabi having feelings for Shougo, but was emotionally conflicted and therefore acting strangely.
However, when Shougo returned to the party, he is lunged by a drunk Miyabi who was eventually rendered unconscious. He took her to a hotel room and waited for her to wake up, which she eventually did. Miyabi first attempted to have sex with Shougo, but she then gave up and cried, asking Shogo to never leave her.
Later on, after seeing the girls off except for Miyabi, who stayed at the hotel, Kanoko Mikadono discussed with Shougo about what had just happened. Her son discovered from his mother that Seri was actually responsible for persuading Kanoko to accept Shougo inviting five girls at once, a revelation that implied a a secret connection between Yuzurina and Seri.