DGKD-314S - 8 Hours of Being Horny for Mom's Voluptuous Ass...

The title mentions butts, but the actual content is pretty much the same as any standard incest AV. There isn't much focus on butt-centric play (there's even some breastfeeding stuff). Basically, it just means the actresses were chosen for having thick, curvy hips. Since they're mostly mature women, which adds to the lewdness, it might be hit-or-miss depending on your taste. That said, for this genre, there are quite a few high-quality actresses here.