First of all, congratz to the developer for such an interesting slow burn NTR. Can easily say this is top ten in my list. Can't wait for the next updates.
Most of the story are great except Beach event especially Beach Doll, which I find it lackluster. IMO, it should be focusing on Shion that dislike of losing to Erica and collaborating with Masaru to bring Erica so she can feel equal or better than Erica. The net part is kinda ridiculous, sorry to say that I skip most of this part.
And I feel that the options for the Masaru ending is kinda weird. I thought it should be combination of Trust/Distrust (Sleep/No Sleep) Shion and Believe/Disbelieve Memory Energy.
1. Trust Shion, DisBelieve Memory Energy (NTR-A ending - Masaru's new wife)
Dan try to trust Shion again and assume all of those are just nightmare. When the last part happened, he stick with his disbelieve to the point of being delusion and just stand with mind broken.
2. Trust Shion, Believe Memory Energy (NTR-B ending - Brazier of Eight)
Dan try to trust Shion again and believe all the past happenings. He still hopes there's a chance that Shion will be back to him, but by trusting Shion, all of the Shion Cheating at the ending are actually happened. When the last part happened, he lose all hope on Shion. Disappointed by her, thus the burning happen.
3. DisTrust Shion, DisBelieve Memory Energy (NTR-C ending - Ultimate Betrayal)
Dan do not trust Shion so he avoid sleeping. He counter the drowsiness with high dosage of caffeine/drugs, but it cause some madness to build up in him. The madness cause him to fully focus on preventing Shion to cheat and success in doing so. By collaborating with Earl, he manage to send away Masaru, thus breaking up Masaru grasp on Shion. He always beside Shion and never rush to buy the ring. Finally, Dan propose to Shion and she accept. Dan believe that he manage to satisfy Shion on bed, but in actual, Shion is never satisfy due to Masaru training and she perfectly hide it from Dan.
After a period of time, Masaru secretly come back and stay in Ram city and contact Shion. Shion after prolong dissatisfaction from Dan's performance, finally decide to cheat with Masaru again. Masaru tell her to remove the ring and put it inside her rectum for him to tarnish the ring by ejaculate in her anal. Masaru give her another rings, nipple pierce ring and clit pierce ring. he tell her to pierce it herself to show her obedience over him and she willingly to do it.
Earl contact Dan and tell him that a few days ago Masaru has gone missing and warn him. Dan having a believe that Shion is satisfy with him and Masaru is away from their life, Dan has loosen his control over Shion. As he remember that Shion need to go to Ram city to buy some utensils, he panic and try to call her but unable to get her. After searching high and low for Shion for a few day, but unable to find her, Dan decide to go back home for quick rest before continue searching. But when he reach home, he is greeted with some long forgotten smell. He go up to their room, but to be greeted by Masaru and Shion having sex on their bed. The whole house has been their copulation chamber for the last few days. Shion decide to tell Dan about her reason for cheating, which cause Dan recall all the past memory, but this time, his dignity as a man is broken as well.
All of this is actually Masaru elaborate plan from the beginning when he fail to open the door with the iron chain. He believe that Dan will never be able to satisfy Shion and she will eventually come back to him. With all this condition, he manage to open the door (OR not. It depend on the developer)
4. DisTrust Shion, Believe Memory Energy (non-NTR ending)
Same with the point 3, but by believing memory energy he realized that he will not be able to satisfy Shion if he do not do anything.
At this point, there are few options.
a. Dan build up his performance and manage to satisfy Shion (kinda happy ending. I believe he deserve a happy ending)
b. Dan decide to contact Masaru and hand over Shion (NTRS. Not my favourite, but I believe some like this)
c. Dan decide to murder Masaru to ensure that he will not come back (Gore. Just gory)
These are my thoughts about the endings. It will be cool if the developer read this and implement some of it.