sarah illustrates open marriage

After Cain’s fight, the seventh match proceeded without a hitch, and as always, Seraph stepped into the ring for the final battle of the round. Though his earlier wins had been desperate and narrow, the prince’s arrival brought a chorus of cheers from the audience. One might expect this noisy support to bolster his confidence and turn him back to how he was, but he remained humble, or perhaps ‘fearful’ would be a better word. Every win would plague him with doubts, doubts that he was really strong enough to have defeated his opponents. All of his accomplishments were surely due to plain luck, or maybe his enemies had been paid off to let him win.

Sarah swallowed; her mouth suddenly dry with nervousness. She was sweating from the strain of holding herself in place, but that sudden slickness gave her an idea. Easing her pressure on the bed her body weight now mostly fell on her father, her breasts crushed against his chest. Pushing forward with her hands her body slipped an inch down her father, and that inch translated to an inch down below. It was more sudden than she intended, her father’s tip pushed fast and hard past her lips and into her dripping pussy. She moaned in ecstasy, unable to hold it in. She could feel him inside her now, stretching her opening and with it, feel the beat of his heart in her most sensitive place. She was on fire.

idk if you've played chaos;head (or watched it, I never saw it so idk if it's in the anime) but it's set in the same world as steins;gate (which I've watched but never played) and things the eyes see but the brain doesn't process are a literal plot point, you could almost certainly make a fairly lore accurate manip with that if you like this world.