Bought it yesterday and I've only unlocked 7 out of 8 characters.
Since English is not my first languaje and I couldn't understand quite well the game, I'll ty to explain how to get the secrets characters…
- The first one is the master. In order to unlock him you have to go the japanese style cafe on the first day and select the first choice (the master will join the scene). Then, when the mc is jerking off on the bed select the second one (master's face should appear). Next day choose to go to the cafe, pick the the blond guy and choose the first option (a cocktail).
- The second one is the swimmer. In order to unlock him you have to pick the first guy in the cafe and pick the first option. On the next pair of choices pick drink (the second one). In the jacking off scene it will not show any character. On the next day pick the fourth character and select the second choice (the banana game).
- The third one is unlocked with the seven digits code that you get through getting endings. The code (examination id) is 2122122 and in order to introduce it choose at the second day to not go to the cafe or the yellow button on the main menu.