Yusaku Sakaishi is a Japanese author known for originating the light novel series Rich Girl Caretaker, which has also been adapted into a manga and an upcoming anime television series. Sakaishi is credited as the sole writer of the original story for this franchise.

The Rich Girl Caretaker series, with illustrations by Sakura Miwabe, began as a web novel that Sakaishi posted on the Shōsetsuka ni Narō website, where it ran from April 2020 to October 2021. Following its success online, the series was acquired for print publication by Hobby Japan, who began releasing it as a light novel under their HJ Bunko imprint in May 2021. Multiple volumes have been published, with at least ten volumes available as of May 2025.

The series expanded into other media. A manga adaptation illustrated by Sorahiko Mizushima began serialization on Hobby Japan's Comic Fire website in July 2021. An anime television adaptation produced by the studio Brain's Base has been announced and is scheduled to debut in July 2026. The anime will be directed by Shūsei Morishita.

Beyond the Rich Girl Caretaker franchise, Sakaishi is also the author of another light novel series, The Holy Knight's Dark Road, which has been licensed for English release by J-Novel Club.