Futari no Tame ni Sekai wa Aru no.

Asukagawa Chiharu is student body president of Ushitora High. Kisaragi Kyou is student body president of Ushitora's rival school, Bishin Academy. That naturally makes Chiharu and Kyou bitter rivals as well, but the relationship they hesitate to flaunt in front of the public eye is one of... lovers! They even have sex at hotels and are an average (!?) couple!!

(Source: ShoujoMagic)

Included one-shots: Valentine Cinema, Joou-sama no Okiniiri (The Queen's Favorite)