Bought (DLsite) and finished Atelier Sakura's swapping game. 8.5/10. It begins as a vanilla swapping game, with two pairs of couples literally dicking about. Halfway through the game, the protagonist is unable to spend time with the group anymore due to a hospitalisation in the family and that is where the game's only choice appears. The game can either continue as a vanilla swapping game until the end (short route) or continue on as an NTR into an NTRS game (this is the true route, long with after credits). This route is quite unique so props to Zuka. It begins as hard NTR where the protagonist sees a hidden DVD recording of his girlfriend (blonde hair, Rina) + the antagonist and his girlfriend doing a 3P. The antagonist girlfriend (purple hair, Mayu) is pretty amazing in her own right, btw. She is totally cool with all the sharing and then the cheating as well. What is amazing about this route is that there is none of the obvious fluster and guilty giveaway that everyone is having 3P adventures without the protagonist. They all act incredibly normal and jokey around him, which really hits the NTR buttons. When the protag tells them straight that he knows what is going on, they all apologise ...... and so does he, because he realises the only reason he didn't say anything before was because he is actually turned on by knowing Rina is cheating on him. The game goes full netorase and the protagonist happily pursues a romantic relationship with Rina, while she happily continues a sexual relationship with the antagonist.
This is not a "vanilla" swapping game, but it is a game where everyone ends up happy with being able to carry out their various fetishes. The protagonist loves being NTR'd. The girlfriend loves cheating. The antagonist loves dominating the girls. The antagonist's girlfriend loves being a masochist to the whole situation.
Game is longer than average for an Atelier Sakura game. However, points are taken off for no heroine perspective and several implied cheating scenes never being shown.