'The Stepmom's Child Was the Ex-Girlfriend') is a Japanese romantic comedy light novel series written by Kyōsuke Kamishiro and illustrated by Takayaki.

Between flirtations and shouting matches for minor reasons, the two students stayed together until they entered high school, where they finally decided to break up.

In order not to hinder their parents' happiness, they accept the situation and decide to put in place the rule of brothers and sisters, according to which the first who feels attraction towards the other loses.

"east head") and Tanesato come from Conan Doyle ("Irido" is almost an anagram of "Doiru", which is the Japanese pronunciation of Doyle), Yukito Ayatsuji (only the word Aya (綾) is taken), Nisio Isin (while Nisio is the surname, it literally means "west tail", the opposite of "east head") and Ellery Queen (while Queen is a duo whose surnames are Dannay and Lee, "Danna-" is pronounced like tane and "Lee" is pronounced like ri ("里" can be pronounced as sato and ri in Japanese)), respectively.

[12] In the Blu-ray set of the anime series, an original what-if story titled Mamahaha no Tsurego ga Imakano datta (継母の連れ子が今カノだった, lit.

The series was directed by Shinsuke Yanagi, with Deko Akao handling the scripts, Katsuyuki Sato designing the characters, and Hiromi Mizutani composing the music.