This requires a fine-tune that already knows NSFW motions - this is just an enhancer

Stomach distention from penetration is a real thing, the anime version of it are generally greatly exaggerated in a way that I find off-putting, so I tried to capture a realistic version of belly bulge.

It's rather finicky. It's a rather subtle effect most of the time, but noticeable when comparing side by side with and without it, but also sometimes it's pretty significant and unrealistic. In general though it avoids the 'anime style' of belly bulge though.