Kakurenbo Battle Monster Tactics (Spiral/Nintendo, 2000)
It's a TRPG with really good music published by Nintendo. It's also kind of long winded in the beginning, so in the interest of time I had to stop before getting to see any combat. Still, the descriptions I've found online are interesting and it seemed promising, so I'm tossing it on the return to list even though I barely saw anything. Worst case it's a very quick return.
Kakutou Ryouri Densetsu Bistro Recipe: Gekitou ★ Foodon Battle Hen (Red 5 Software/Banpresto, 1999)
This incredibly long title goes to a game that asks "what if Pokemon, but food and also cards?" which was not something anyone else cared about. There's really very little to say about it that isn't covered by "bad Pokemon clone."
Kakutou Ryouri Densetsu Bistro Recipe: Kettou ★ Bistgarm Hen (Red 5 Software/Banpresto, 1999)
If, like me, you assumed this was another version of the same game since they're Pokemon clones that came out in the same year, then we're both wrong. Despite releasing barely two months after the other one, this is actually a sequel that, unsurprisingly, changes basically nothing. It's most notable for somehow thinking that enumerating every single one of its characters in the intro scene was a good idea and that anyone would remember than for more than 10 seconds.
Kanji Boy, 2, and 3 (J-Wing, 1999, 2000, 2003)
Three different versions of essentially the same kanji study game. The first one takes a solid minute to actually load in the questions, which for a GBC game might as well be six years. The other two are essentially the same game with three more difficulty levels. Easier ones, oddly.
Kanji de Puzzle (MTO, 2000)
Another kanji study game, but this one is on an extremely short timer.
Kanzume Monsters Parfait (Airsystem Tokyo/Starfish, 1999)
Tamagotchi, but instead of a cute pet you have a monster who lives inside a partially opened can. I guess someone wanted that.
Karamuchou wa Oosawagi!: Okawari! and Karamuchou wa Oosawagi!: Porinkiis to Okashina Nakamatachi (Starfish, 2000, 1998)
If you can tell which of these is which, then you're probably doing better than anyone except the developers. They're two puzzle platformers with completely identical intros and level select screens, although the levels themselves are at least a little different. These came out two years apart, so it's not like they were meant to be Pokemon versions or something.
Golf Ou: The King of Golf
John Romero's Daikatana
Kakurenbou Battle Monster Tactics