At least 20 points in law (治世) or chaos (覇道) is needed by the end of chapter 7 to see their respective route. If you have less than 20 in both, you will see the normal ending, which immediately ends the game. If you have 20 in each, you can decide between law, chaos, or normal. Having a significant amount of chaos (approx. around 25 to 30) will lock you into the chaos end regardless of how much law you have.
At the end of chapter 7 is the one spot in the game where enemies do not attack you, so that is the ideal time to get the events from the last goddess or two that hasn't been around long. If you played the game up to this point, you could access any ending from this point if you:-
i). Without corrupting any of the goddesses or getting them to 99 friendship (親交)
ii). Keeping law and chaos relatively balanced
iii). Amassing favorably (好感度) with all the girls.
Goddesses are corrupted when their tainting value (調教) increases to the point that divinity ratio (神性比) reaches 0%.
A note, at the beginning of chapter 6, the three sisters leave you, and you may be locked out of their ending if you didn't get their Favor high enough. (Getting Favor to 2 before the end of each chapter will allow you get them back later in Chapter 7 when you defeat each of the sisters to get back the captured Goddesses).
Reaching 99 points in friendship and amassing favorably of 3 with a goddess before you corrupt them will give them 2 skills of your choice. This unlocks an ending for them in the law route but prevents any further sex scenes with them until the end.
To get individual endings, you must have a favorably of at least 6. In the law route, there are 2 endings for each goddess; i). If they are corrupted or ii). An ending with the three sisters if you have a high favorably with all of them. The law's ending changes slightly depending on if your final chaos is higher than your law or not.
In the chaos route, there are 2 endings depending on whether you corrupt the 4 goddesses further or not.