https://booru.allthefallen.moe/posts/52183
https://booru.allthefallen.moe/posts/287333
Basically it's like an extreme variant of piledriver where the "driver" is squatting deeply and sitting their hamstrings (and maybe glutes) atop the hams/glutes of the "driven" person lying prone on their back underneath.
It gives the sense of "I'm using more of my bodyweight to push them into this position" as opposed to "relying totally on my arms and their own weight" which is what you usually see.
Seemed to stand out as pretty interesting to me and I doubt I'm the first, but I don't know how obscure any japanese tagging for this might be (like maybe pixiv only if it's not on gelbooru? lots of pixiv stuff hasn't made it to gelbooru yet)