Kakushite! Makina-san!!

Synopsis

From Seven Seas: Gloomy high schooler and robot otaku Akutsu Eita comes home one day to find his school’s idol, Agatsuma Makina, right outside. A lucky break for Eita, especially when he finds out that she’s a robot created for sex! The virginal Eita is thrown through a loop by how physical things suddenly start getting. But while Makina wants to bare it all, including her robotic interior, Eita has to keep her identity a secret doesn’t he?

Synopsis & details from MangaUpdates