Imouto is possibly the first planned rival in Yandere Simulator. For now, her AI is not complete, so you cannot interact with her. At the moment, she stands behind the first blossom tree on the left of the school entrance.
In an older intro, you see Imouto being very rude to Senpai after Yandere-Chan runs into him. She implies that she is a childhood friend of Senpai during the conversation. Later in the intro, you will meet Info-Chan, who says her name is Osana Najimi, which means "Childhood Friend" in Japanese. However, this name has been overwritten with the present name.
Fan Theories Edit
Fan Theory #1 - Female Senpai: Edit
Some fans of Yandere Simulator believe that you will be able to customize and choose if your Senpai is male or female in a future build. If this happens, fans think that Imouto will be a female Senpai. However, in the first intro programmed into the game, it shows a screen where you can customize your Senpai, and a feature where you can choose their gender.
Fan Theory #2 - Senpai's Sister: Edit
This theory also features Senpai. In this theory, fans think she is Senpai's sister. In the older intro, she implies that she is a childhood friend. With her quote "You've been like this since we were little kids." that was directed to Senpai, some fans thought she might have been related to him.
Fan Theory #3 - A Rival: Edit
This theory is arguably the most popular theory revolving around Imouto. There is sustainable evidence that she is indeed the first rival. First of all, if no one in the school is alive by Friday except Yandere and Senpai, a student will confess her love to Senpai. This makes Imouto the only possible student that could be the first rival. However, this theory was never confirmed and not necessarily true.