Oshi no Ko & Kaguya-sama in the Same Universe, a Few Years Apart
The official Twitter account for the manga series Kaguya-sama: Love Is War, with the username @kaguya_comic, revealed in 2021 that Kaguya-sama: Love Is War is set in the same world as another manga series by Aka Akasaka titled Oshi no Ko.
Even though they are in the same universe, Oshi no Ko & Kaguya-sama have a time difference of several years, which is not specifically explained.
【第3回「かぐや様目安箱」】A.007 赤坂先生より
— 漫画『かぐや様は告らせたい』公式@最新23巻 発売中&実写映画“ファイナル”超大ヒット公開中! (@kaguya_comic) August 26, 2021
☆【推しの子】は『かぐや様』より何年か後の時系列で、生徒会メンバーも社会人になってそうです。 https://t.co/pzG5nHEUDo
"[Oshi no Ko] is set several years after Kaguya-sama, and it seems that the student organization members will also become members of society."
With the published tweet, it can be concluded that Oshi no Ko and Kaguya-sama are in the same universe with a time difference of "several" years.
After the statement came out from the official Twitter account for the Kaguya-sama: Love Is War manga, some fans began to speculate that the Oshi no Ko character named Frill Shiranui might have something to do with the character Koromo Shiranui from the Kaguya-sama: Love Is War series.
In fact, the descriptions of the way the two enter class are also quite similar to each other.
Meanwhile, Aka Akasaka began serializing Kaguya-sama: Love Is War manga (Kaguya-sama wa Kokurasetai) since May 19, 2015. The first volume was released on March 18, 2016.
Although the status of the manga Kaguya-sama: Love Is War is still ongoing, Aka Akasaka unexpectedly decided to create another new manga series titled Oshi no Ko in collaboration with Mengo Yokoyari as the illustrator.
For your information, Mengo Yokoyari is a female mangaka famous for her manga titled Kuzu no Honkai, which was serialized starting from September 25, 2012. The first volume was released on February 19, 2013, while the eighth and final volume was published on March 25, 2017.
Together, the two began serializing the Oshi no Ko manga in Weekly Young Jump magazine on April 23, 2020. The first volume was released on July 17, 2020.