My Little Sister is Disciplined and Beautiful! (妹は、規律正しく美しく！ Imōto wa, Kiritsu Tadashiku Utsukushiku!) is the 7th episode of the Kono Naka ni Hitori, Imouto ga Iru! anime series.
As Konoe Tsuruma and Miyabi Kannagi became increasingly intimate with Shougo Mikadono, fuelling the boy's fear of of whoever he chose between the two as his wife could be his biological little sister. Ikusu Mizutani suggested using DNA testing to find who really was Shougo's sister. The test would be conductied with the help of Risa Seri, Kanoko Mikadono's secretary, to avoid speculation from the public.
Some time later, Shougo received the DNA sample taking toolkit from Risa. It required him to take saliva samples with cotton swabs. While Konoe agreed on taking the test, Miyabi declined and wrongly thought Shougo was a fetishist.
A board of directors come to inspect the academy's performance, and Shougo was called to meet them due to the request of Genda . During the meeting, Shougo's little sister made an announcement over the intercom to blackmail Shougo. She threatened to expose his secrets if he continued his effort to uncover her identity. However, she also told Shougo to be wary of his surroundings.
Shougo later found out that neither Konoe nor Mei Sagara had the voice-changing cellphone with them during the incident. Mei, however, had thrown her phone away by accident, thus Shougo and Ikusu ssuspected whoever made the call must have had found the prototype phone. Said person, who could use the voice-changing function, could only be among the five girls whom Shougo had previously told his story to.
To response to the call during the meeting, the student council appointed Shougo as a morality officer to enforce the conducts of students. Shougo was chosen particularly because the board of directors had eyes on him, as well as his popularity to other students. Suspecting of Rinka Kunitachi's absent during the meeting, Ikusu advised Shougo to use his new duty as an opportunity to observe Rinka.
Rinka, with the assistance of Shougo, tried to correct what she saw as 'imroper behavior' on part of the students. She also became increasingly agitated and jealous of Shougo's popularity to the girls.