Choose one guy at the beginning and stick with him, gift him everyday if possible (Rald likes the perfume, Kovit likes the watch, Sota likes the wallet and Remi likes the designer shirt), go out on dates everytime and search for them in different places if you can't find them in their usual spot, always pick the one at the spa and always give the most polite and kind answer, they all like when Tomoki show interest in them and what they do. This would unlock almost everything in my experience (apart fromy the bad end for the guy obviously)