I know that he can initiate it as a random event. You probably need to be submissive and/or have low respect for that, but I can't be sure of that (or I saw the submissive/low respect variant?). No idea if there are other scenes.
Viewing post in Lust Odyssey (NSFW Visual Novel) comments
I made a separate save file where I sabotaged my respect by fighting Bradley repeatedly and getting into the fighting pit orgy. I managed to lower my respect into the negatives and then was able to find the sex scene with Gravel. So yeah that pretty much confirms you need negative respect for that. However, I am surprised that Gravel still hasn’t had his artwork finished.
I haven’t played through everything yet, but the two events I know for sure are killing the wyverns for the refugees to gain respect. And fighting Bradley again to loose respect.
With killing the wyverns for the refugees, they will pay you a little for each wyvern you kill. They can only pay you for the quest once a day, but then offering to fight the wyvern again the same day will grant you respect. You can repeat this to get money and respect every day. However, after you defeat the Warlord, the quest is no longer available as far as I know.
Hm, does losing to Bradley again affect crew respect or just area respect? It was actually pretty difficult for me to figure out how to get from -38 to -40 crew respect and I'm wondering if I missed opportunities to farm negative crew respect.
EDIT: Oh, I can still repeat it even though the dialogue makes no logical sense after defeating the Warlord. Still reduces area respect, but doesn't seem to change crew respect.
EDIT again: Seem to have hit the limit, though. I'm at -24 area respect and don't really know how to decrease it any more.
I only very recently discovered this game, so my experimentation is still fairly limited. However, I would imagine that there would be some sort of threshold on losing or gaining respect. Like once an area gets to the lowest respect possible, it doesn’t really make much sense to be able to lower it even further, when you don’t get any extra scenes or behavior from the inhabitants. I mean, there can only be a finite amount of variations that the developer wrote based on the respect level. He probably didn’t want people to feel like they were wasting effort by continuously lowering or raising respect more and more when there was nothing new for them to unlock after reaching the threshold.