Seisui Kakumei: Omorashi Seijo wa Sono Seisui de Musou suru

"Basically, the holy water is pee, right...?!" Since she dropped out of school because she peed her pants, Suzuna has been helping her older sister, a manga artist, by working as her assistant. One day, after staying up all night, Suzuna loses her footing and falls down the stairs... Suzuna thought she was dead, but she finds herself reincarnated as the saintess in her sister's serialized series, "The Saintess's Holy Water is a Panacea and Unrivaled in Another World"...!? An isekai tale of peerless pee begins!! (Source: Takeshobo, translated)