The manga follows high school student Hotaru Tachibana, a girl disguised as a boy. Through strange circumstances she finds herself drawn into the world of survival games by a host, Masamune Matsuoka. The two form a team with ero-manga artist Tooru Yukimura and aim to be the be the best in Japan.(Source: ANN)

From The Zero Alliance:
Prequel Oneshot:
Matsuoka and Yukki were close friends who dreamed of becoming professional soccer players together. But their hopes were dashed when Yukki moved away due to family issues.
Years pass and Matsuoka is now a host while Yukki has become a hentai mangaka. Matsuoka meets Yukki again while the latter is fleeing from his editor, and is soon introduced to his childhood friend’s latest obsession…
Sequel: Two-Part Oneshot & Series:
When Hotaru moves into a new apartment alone, there’s a mysterious man standing nearby the apartment. Hotaru decides to confront the man, who turns out to live in the neighbouring apartment. The next day at school, Hotaru’s best friend Kanae tells Hotaru that a host tricked her out of her money. When Hotaru goes to confront the host, he happens to be none other than Hotaru’s neighbour, Masamune?!