Fastest way ingame is playing the Stone, Paper, Scissor game.
Always choose the same one, I usually choose the one on the far right as it overlaps with the 25$ marker.
Treat a loss as a -1, a draw as 0 and a win as +1. Save every time your total is +1.
If you get a -1 or 0 keep playing until you get to a +1 total.
If you ever have a total of -2 reload save.
You could of course use a save editor for ex.
You must be registered to see the links
.
Or use Maim Lains Cheatmod
https://f95zone.to/threads/milfy-city-lains-walkthrough-cheat-mod-v0-6e.41364/.
Good Luck