At last, I got the ending for Kei! Was quite a journey to get to a good relationship with her and I'm very happy we got to know her better as well as having... quite, quite an interesting ending.
"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."