All Quiet on the Sister Front is the one hundred and fifty-seventh chapter of To Love-Ru.
A boy (Ooyoshi from C-Class at Mikan's school) asks Mikan out, but she turns him down, to the amazement of her friends. When they ask her why, she says that she is not interested in dating, but blushes when they mention Rito.
Back at the house, Mikan thinks about what her friends said, while Rito and Lala play each other on a wi-fi video game. Mikan sees Momo and how close she is to Rito (obviously flirting with him), and confronts her about it. Momo promises that she won't sneak into Rito's bed anymore, but Mikan is not convinced.
That night, Mikan sneaks into Rito's bed, to catch Momo if she came into Rito's bed. She never shows up, and Mikan looks at Rito's face with love, until he grabs her butt in a dream about marshmallows. He eventually lets go, and Mikan begins to head back to her room when a thunderstorm starts. Rito, in his sleep, hugs Mikan and says, "Onni-chan is here," like he used to when they were kids and Mikan would get scared. Mikan realizes that the thing that calms her down is the smell of her brother, showing her brother complex towards him.
The next morning, Rito finds Mikan in his bed. Mikan tries to explain, but is interrupted by Momo, who snuck in Rito's room in the morning. Momo asks Mikan who it was like, sleeping in Rito's bed. Mikan quickly denies this, and Rito stands there, bewildered by the confrontation.