Just played しゅきしゅき!シスターマリアンヌ (
https://www.dlsite.com/maniax/work/=/product_id/RJ281620.html).
It supposedly has NTR in the latter half of the game, though it doesn't have the tag on Dlsite.
The game is pretty confusing and kinda buggy but the heroine is pretty erotic and the art ain't bad. After checking the maker's Ci-en, there's a walkthrough for the first half of the game (which isn't NTR) and they're gonna post the walkthrough for the second half next week or 2. Problem is, the game is really confusing even with the walkthrough because its so non-linear and the time system is annoying.
The first half is simple once you know what to do. Talk to two kids in the house above yours and get a bunch of stuff (one kid gives sleeping pills and the other gives tea. Just keep spamming the interaction to get as much as you want). Another kid in that house teaches you how to grope the nun, I think. Then go back to your house and talk to the dude beside you to mix the pills and tea together. Do it repeatedly since you'll need more than one mixture. Around 5 will do. Grope the nun three times and she'll start to like it. Talk to the kid to the east of the church repeatedly and he'll tell you how to peep into the nun's bathroom (just interact with the wall beside the kid). At night time, talk to the only kid awake (he's in between your house and the one above). Talk to him again when its a bit later (around 11pm) and he'll give you a key to get into the church at night. Now you can visit the nun in her room at night (its the only room you can enter). The thing is that there's another nun patrolling and she'll kick you out if you step in the wrong place. An NPC tells you where to step to reach the nun but its a pain in the ass. A skip around this is to simply go to the nun's room before night time since the patrolling nun will only evict you at night. Stay in the room until 7pm and the nun heroine will arrive (you can skip some time with the item you get in the chest at the start of the game). Give the nun some drugged tea and she'll sleep. Grope the hell out of her. The next day, do the same thing, but this time there'll be a new option for sleep sex. Repeat the event the next day and the day after. She should wake up and catch you in the act. After that, if you interact with her outside where she normally is, you'll get another option for an h-scene. You can also visit her at night again for a blowjob, or drug her again, but I'm pretty sure that does nothing to advance the game.
That pretty much makes up the first half of the game. It took 2 hours to find this shit out. After you do all that, HOPEFULLY on Tuesday mornings, the nun at the altar in the church will send you on an errand with the heroine to the town next to the church. Just accept her errand and meet up with the nun by the exit. I don't know how I was supposed to know to talk to an NPC that says the same thing over and over again on a Tuesday morning and I don't think I would have ever found out if it wasn't for the Ci-en walkthrough. Sad thing is that's where the walkthrough ends so I had to do everything on my own after that. Going to the town, you'll split up from the nun and be tasked to talk to the two store owners and the errand will be over. This is doable every Tuesday morning, just make sure to talk the the nun heroine before 10am or she'll have done it without you (so you'll need to wait till next Tuesday). While on the errand, you can go to the bar and talk to two NPCs (they both trigger the same scene). They'll mention that a nun is going to blow them outside. Go outside and you'll see where to begin the scene. Its a repeatable scene and also the only NTR scene I've managed to find.
At this point I don't know what else to do. You can go to the lower area on the world map and talk to some black dude. You can also recruit him and bring him to the heroine at her usual spot. This will allow him to stay in the church. He's always at the same spot in the church and leaves with everyone else at night. I don't know what he's there for but you can make him leave the church and he'll go back where you found him. You can always take him back. There's also the confession booth to the left of the church. On Fridays before night, you can talk to a nun there (presumably the heroine). The dialogue advances and you'll be able to tell her about your sinful feelings for the nun heroine, though this hasn't changed anything and its repeatable so I don't know if it even matters. There's also a clown in the bar that mentions a NTR event in the second floor in the inn, but I think you need to have the nun get NTR'd by a specific guy before that event will happen. Strangely, the inn doors are always closed, but when you do the Tuesday event with the nun and you split up from her, the second door in the inn will be open, however the MC can't enter. This might be a bug or I still need to do something.
That's all I got. Its supposed to be a short game so I don't want to wait an entire week for a walkthrough. If anybody knows how to get anymore scenes, please tell me. I didn't expect to suffer so much from this game. You can argue that the NPCs give hints for what to do but its a bitch to decipher them with a translator and the time system is a bitch.
Shine