Have a full set of the maid outfit.
Train Gin a few times with the maid outfit, now after all of that. Train Gin as a maid and DON'T sleep, go in and out of the abandoned town area; AT -> NA(repeat) until Gin disappears from his spot.
Go to Cassie, repeat the steps above proper until Cassie goes to the pond in the forest. Cassie can go to a milk run, apple harvest, or fishing, you need her to fish.
When Gin is trained with the maid outfit, and Cassie meets him again after the first clash then Gin's route will progress.
The checks are:
1. Gin was recently trained with the maid outfit.
2. You caught Gin wearing his maid dress at the pond.
3. Cassie already caught Gin there once.
Afterwards maybe he'll be in the desert.