Chikan densha: Oku made tsumete (1981)

Starts with this slim blonde chick in a diving mask and snorkel, spoon in hand, looking like she’s about to mess with you. She’s got long straight hair covering half her face and a couple tattoos on her thigh—petite but not shy. Then there’s an Asian girl with a short black bob, sitting on the beach in a swimsuit, holding a drink like she’s just chilling. No action yet, just build-up. Cut to the real deal: the blonde’s on her knees, sucking or jerking off some dude while the Asian girl’s right there, either watching or joining in. Camera’s low, so you get a good look at everything. Later, the blonde’s solo, touching herself with her tits out, face blurred but the rest is clear. Dark lighting keeps it moody, but you see enough. Not a ton of positions, but the oral and hand stuff is solid, and the mix of the two girls makes it worth it.