I'm not sure if I'm doing anything to trigger it, but it seems the first ending can be obtained by getting her to max obedience(I assume is what it's called, bar on the right).
Unlike other interrogation scenes, it seems that looking at her panties will ALWAYS increase obedience, looking at her face ALWAYS increases the her patience(the stat that shows how much she tolerates you doing things to her that every game has) and looking at her boobs lowers that tolerance and doesn't do anything else.
There will be a counter of 1-4 in the middle of the bars, this seems to be the stage of the conversation you guys are having. Once she asks a question it will increase by one, by the time it hits 4 there's pretty much nothing more to be said. Having her at MAX obedience, your character gets an erection and she kinda stands over you and you get a lot of options.
A non-colored dialogue option will keep you guys talking with eachother, at this point you can select an H scene. I don't know what the top 2 are, but below that is a handjob, then thigh job, then blowjob, then foot job. If you click the first red option, you pin her down(I think the genre is called domination loss when, when fendom is reversed partway through) and this gives the rape end. will experiment further. Looks like the bottom red option is just doggy style but still a rape end.
Getting the rape end unlocked a special end at the bottom for me, but so far it seems to be the same as the regular mode. (seems to be a free mode, I could H her from the start).