This is a response to a comment by a visitor to this site. The visitor asked why Kai won't visit the Valley in other seasons if you have unlocked the Mineral Town visitors by inserting FoMT/MFoMT into the GBA slot with HM DS or HM Cute DS.
Well, Kai is a guy who only loves Summer and refuses to work in any other season. In FoMT/MFoMT, his beach shack is open for business only during Summer. Likewise, in HM DS/HM Cute DS, he opens his stall on the beach in Forget-Me-Not Valley only during Summer. He may or may not open a stall or cafe on some tropical Island during the other Seasons... there isn't any Harvest Moon game at this point in time that features Kai working in Spring, Autumn or Winter in ANY location.
One does wonder sometimes how Kai manages to work BOTH at his seaside cafe in Mineral Town AND at his stall at the beach in Forget-Me-Not Valley simultaneously during the Summer seasons, but that is a problem in logic that is overwritten by the singular rules of magic embodied in Harvest Moon.
Incidentally, if you marry Kai in HM Cute DS, he will stay in the Valley with you, although he will maintain his philosophy of working only during the Summer season. One suspects therefore that he would not work ANYWHERE in Spring, Autumn and Winter, even in the hottest of climates, but who knows...? Harvest Moon is a saga that we hope never will come to an end.
Where all other visitors from Mineral Town are concerned, their patterns of movement follow ordinary logic: they visit Forget-Me-Not Valley on their 'Days Off'. Thus, Grey visits the Valley on Thursdays when the Smithy in Mineral Town is shut. Karen visits on Tuesday when the Supermarket in Mineral Town is closed. (The Supermarket is shut on Sunday as well, but Mineral Town visitors, apart from Kai, are allowed only one visit to Forget-Me-Not Valley per week.) And so on...
There is a game that may appear in the future where characters from Mineral Town visit an Island on a seasonal rather than weekly basis... but more about that in a month or so.