Reichu wrote:While masturbating with the core makes perfect sense, figuring out how the "crotch fin" plays into things is another matter entirely. My only possible guess is that the Eva is using the fin as a handle to wobble the pelvic plating back and forth, thereby generating friction against whatever precisely is underneath.
I must praise your ability to make any weird situation even more WTF by the power of analyzing it in all seriousness, it's a talent.