u/Wonderful_Bank_8429

I'm envisioning a larger but more submissive boyfriend and a smaller but more dominant girlfriend. The boyfriend does better with most physical objectives (moving heavy things, accessing new areas, etc.) while the girlfriend does better with most social objectives (interactions with NPCs that require persuasion, distraction, etc.), but not exclusively; some physical objectives will be better suited for the girlfriend and some social objectives will be better suited for the boyfriend.

Trial and error will come into play when some methods of progression fail, which will affect the route. If you come to, say, a gate with a guard in your way, you could play as the girlfriend to either distract the guard or sneak through a hidden crawlspace that the boyfriend wouldn't fit through. The crawlspace option would be quicker and easier, but the girlfriend would protest against it, vocally preferring to do the dialogue option. By taking the crawlspace option, there would be more tension between the girlfriend and the boyfriend going forward.

The bond wouldn't be measured on one single metric. Ideally both characters would have different stats regarding how they feel about each other.