The (Korean) song is Chocolate Cream by LAYSHA, which is quite good. However, there's occasionally some distracting boob vibro-jiggle, as if you'd twanged a ruler on a desk.
The two girls are Jean Gunnhildr and Lisa Minci from Genshin Impact, an action RPG computer game. Jean's the knight, while Lisa's the one in the purple corset and witch's hat. The costume design is pretty cool, actually, although after a while the girls aren't wearing anything, but the background's just a sort of lava blur.
The second episode is just a sex scene for Lisa, without music or dancing. There's no plot or dialogue, of course, although a voice actress does make sex noises.
The song's PiNK CAT, by GARNiDELiA, which is good. (Song quality is always the most important thing with these MMD videos.) The dancer I think is Kanade Hayami from The iDOLM@STER Cinderella Girls. She's outdoors at night in a children's playground, it's snowing and she alternates between dancing (reasonably well) and having sex.
Episodes: 1 x 4 minutes
One-line summary: CGI hardcore porn
It's late in the office and someone's having sex. When the security guards come round, though, Liz is quietly working at her desk and properly dressed... but only from the waist up.