Misa Amane's sister is a character from the Death Note universe that is only briefly mentioned by Misa and Aiber during Misa's interview at Yotsuba. Although, there's been plenty of speculation regarding this character (some fans say she doesn't exists and was just something Aiber made up for the scam), it is a recurrent character in many fanfictions.
Aiber (as Coil): You have a sister in Kyoto, do you not? You want to protect your image as an idol, so you kept this to yourself except for your sister"
Misa: ... My sister said that?
Aiber: She lets her guard down a bit after a few drinks, doesn't she?
Misa: You talked with her?
Aiber: She probably wouldn't tell you about what she said that night... And she didn't tell this to me directly, of course. But it is accurate information we can see it written on your face.
—extract of Misa and Aiber's conversation at the Yostuba interview.
Very little is known about Misa's sister, except that she tends to be talkative when drunk.
- Asa Amane, the main character in Shatter ME!, is Misa's older sister and a police officer, member of the NPA. She's described as no-nonsense, brilliant behaviorist, skilled in profiling people.