I'm having trouble with finishing Gin's training, I've gotten to the point where he can be trained while wearing a maid outfit
Train Gin, go in and out of Abandoned Town till he goes to the forest area where you can fish;
Gin needs to be trained with the dress on that same day, do not sleep.
Gin needs to be caught by you, twice; with dress, without dress.
Cassie needs to have caught Gin naked on that fishing spot.
Explain to Cassie what's going on afterwards.
Then the route continues.