You unlock Akihabara on September 1st. The maid café is a location in Akihabara near the entrance where you can spend a time slot to gain kindness and charm along with some stamps used to access the special menu. Once you get 20 stamps and come back, you'll get the trophy. I saved before starting this, and reloaded my game after, since I had no plans of spending that much time there naturally. It only took me a few days to get 20 stamps. I was ordering the 5000¥ dish, so I'm not sure if that's why I got stamps faster, but you might as well. If you're genuinely using the maid café for charm and kindness rank ups, the 5000¥ option makes additional kindness points more likely, as the maid will be more likely to mess up the order.