two questions
1. Are you able to download this game on iPhone
2. Are you able to have sex with darci at any point in the game I would really like to know
1) download the game to an iphone? no, however you can technically play the game on your phone if you use the steampowered feature: steam link to stream the game to your phone by having that game as a non steam game in your library. only downside i had was the back up feature not available. Might be able to get back up to work with a blue tooth mouse w/ touch assist enabled.
2) play and find out :)