I have done it! I have managed to complete hard mode! Man, the game devs make it so hard XD I'm happy I was able to learn a lot about Kei and be eligible to go out with her. We just have a fair amount of days left!
"The player (that's you!) is a part-timer who lives an uneventful, boring life. One day, you win the prize draw at the shopping district. The prize: a trip to an island in the south -- you decide to take a 30-day vacation. 'I... want to make this a nice vacation...! I want to change myself in this trip!' You decide to grow out of your dull, boring life and get a girlfriend."