Saw there was still no walkthrough (unless I missed it) so here is the big TL;DR of what you need to know.
For ending...There are 20 yes. Only 6 really matter if you came here for the H though (unless I missed a good one).
You have one main heroine and two subheroine. 2 of the ending are basically the subheroine route. To get subheroine route, just go see her every night as much as possible while doing any random training to Ayame during the day.
For every other ending, you can safely ignore the two subheroine. They don't matter. There is no interaction between the heroines and no threesome possible.
Ayame has 5 stat that really matter: overall nasty degree, "service" degree, "bdsm" degree, "shame" degree, and affection.
To get one of the "good" (read: lewd) ending, you need a high nasty degree by the end. It is super easy to reach. Just make sure to train Ayame every day and you'll reach it automatically.
Once you're confirmed to get a lewd ending (there are 12 of them), the game will look at other stat:
- What kind of training did you do? You have 4 possibility: mixed, service, bdsm, shame. To keep it simple, if you want to get service ending, just do service training during the whole playthrough (same for bdsm/shame). If you want to get mixed, do service then bdsm then shame then service again then bdsm etc.
- How much does Ayame love you? There are 3 possibility. True love, like but no love, and indifference/hatred. From what I saw, there is no real reason not to go for true love. It's the same CG, but true love ending is longer and hotter imo. It feels like they designed the true love ending first then make the other two by removing stuff from true love ending.
How to get true love? Easy! Just get over 100 affection point. Ayama is super easy to romance. Here are the main points:
- Go see her every night. Never skip.
- On first day at night, choose to talk to her (ie, do not rape her)
- Generally speaking, if she asks you to do something, do it.
- On 8th day, stay with her when she is sick. She loves you now, she just doesn't know it yet.
- On 16th day, you should be able to have consensual sex with her.
- Make sure to have consensual sex with her twice (ie, over 2 different day). This should ensure that you have well over 100 affection point. This might be the "hardest" requirement here, since once you saw the scene you might just decide not to see it again and thus miss the "need to see it twice" requirement.
Anyway, that covers the 12 lewd ending + 2 subheroine ending so that makes 14 out of 20. The last 6 are various "failure". There is some for early failure (ie, becomes clear you are so bad at training there is no point), some some late failure, some for if you refuse to train her altogether. Exact ending depends on how much she loves you.