Yumemi Hoshino is the heroine of Key's "kinetic novel" Planetarian. She is a gynoid resembling a little girl who meets a nameless junker in a post-apocalyptic world.
In this wiki, Hoshino is mainly known for appearing in International Saimoe League's 2017 main tournament and its several secondary events. This is likely because of her associaton with Key, a company with a long-standing influence and fan presence in ISML.