Found something out by complete accident that didn't appear to be covered here yet. After you unlock the ability to do foreplay with the main girl, when you hit the 'sweet spot' for the bar to fill click on the lock, then leave the game on and go do something else. Whatever stat that's highlighted, mouth, boobs, etc., their circles will continue to fill even with the lock. Can be useful if you're struggling maxing out the various body parts.
Decided to add more to this post. Grind cash for the special drivers license as soon as possible (sold at the sex shop). It unlocks a mini game where you can farm the special coins you need to buy outfits. Once you obtain the license though, head to the park in the morning and talk to the man on the bench, he offers upgrades for that mini game such as the amount of coins you gain per hit or your truck speed. Upgrade the former (the coin amount per hit) a couple of times then do the minigame. If you’re able last long enough you can get over 500 easy and maybe to or well over 1000 depending.
As long as you don’t overdue your stress meter, you should be able to play this game multiple times at night, and time never moves forward. So with your winnings head back to the park at nighttime and go to the restroom where a bald guy in a trench coat is standing against the wall. He trades 50 coins for 10000 yen so do that exchange a couple of times and you’ll nary have any money troubles and can focus on other things. If the bald guy isn’t in the bathroom, just try the next day.
I’m pretty sure most people here know all of this by now, given how old this game is. Still, figured I should put my two cents in regardless, and share some of the things I’ve learned or realized in my time with the game over the weekend.
Quick update: You’re only able to do the driving mini game once a night, even so, if you’re able to score high on it that’s a lot of money in your pockets when you cash in.