Chikan densha: Hassha ôrai (1981)

This one starts with a skinny brunette in tight clothes crammed into a busy train car. She’s got this anxious look like she knows what’s coming. A guy behind her starts groping her under her skirt, right there in public. She doesn’t stop him — just bites her lip and takes it. Eventually, he pulls her panties aside and fingers her while people are all around. The way she tries to keep a straight face is hot. The camera angles make it feel like you’re part of the crowd, sneaking glances at what’s happening. By the end, she’s leaning back into him, clearly into it. No holding back here.