, also known as for short, is a Japanese light novel series written by Muku Shirai and illustrated by Minori Chigusa. It is based on a series of videos released on the "Kanon no Renai Manga" YouTube channel, with the novels being published under Fujimi Shobo's Fujimi Fantasia Bunko imprint. Eight volumes were published between November 2021 and October 2024. A manga adaptation illustrated by Shokichi Sakai began serialization on the "Nico Nico Seiga" and "KadoComi" websites under Fujimi Shobo's "Dra Dra Flat" label in November 2022, with the series being compiled into six volumes as of April 2025.
Plot.
The series focuses on Ryōta Majima, a man who long wanted to have a younger brother. He gets his wish after his father remarries, leading to having a new younger brother, Akira Himeno. Ryōta wants to be closed to Akira, although this does not go well at first. One day, while taking a bath, he discovers that Akira is actually a woman, although this does not deter his desire to become closer to her. Meanwhile, over time, Akira develops feelings for Ryōta.

Akira's new stepbrother after her mother's remarriage. He has long wanted to have his own younger brother and was looking forward to life with Akira. He also wants Akira to fit in with their new family. Even after learning that Akira is actually a girl, he continues his desire to become close to her.

Ryōta's new stepsister, who has a shy and tomboyish personality. Because of her boyish appearance, Ryōta initially mistakes her for a boy. She later develops feelings for Ryōta.

Ryōta's best friend who has a lazy personality. Despite this, he cares for Ryōta and helps him get closer to Hinata and Akira.

Kōsei's younger sister who deeply cares about him.
Media.
YouTube series.
"Jitsu wa Imōto Deshita" began as a series of voiced manga videos posted on the "Kanon no Renai Manga" YouTube channel. Ten of these videos are currently available as of December 2024; the first two episodes are no longer available.
Light novel.
A light novel series adaptation written by Muku Shirai and illustrated by Minori Chigusa began publication under Kadokawa's Fujimi Fantasia Bunko imprint in November 2021. The series ended with the release of the eighth volume in October 2024. A promotional video featuring Maaya Uchida as Akira Himeno was posted on December 10, 2021.
Manga.
A manga adaptation illustrated by Shokichi Sakai began serialization on "KadoComi" and "Nico Nico Seiga" services under the "Dra Dra Flat" label on September 1, 2022. The manga has been compiled into six "tankōbon" volumes as of April 2025.
Other media.
A series of voiced comics featuring Uchida, Yoshitsugu Matsuoka, Shun'ichi Toki, and Marika Kōno was posted on the official Kadokawa YouTube channel. An ASMR voice product with Uchida reprising her role as Akira was released on April 19, 2024. Art from the series was also included in a compilation of illustrator Minori Chigusa's work that was released on October 19, 2024.