This is set in game canon mostly. I have watched the English anime, so there might be some similarities to the anime, but this is mostly game canon.
Chapter 1: Tears of Madness, Insanity's Sorrow
Kirby was taking a walk through a forest. It seemed like a nice, peaceful day.
Suddenly, Kirby heard someone crying. "Poyo?" He looked around to see where it was coming from. It was Whispy. Kirby ran up to him. "Poyo?" He was asking "what's wrong?"
Whispy didn't answer. He simply ignored Kirby and continued weeping.
Kirby doesn't like it when friends are sad, so he tried his best to comfort Whispy, but to no avail. No matter what Kirby did, Whispy wouldn't even acknowledge Kirby's presence. Kirby finally decided that maybe he should just give Whispy his space. Maybe he just wants to be alone. Kirby began walking back to his house. On his way back, he noticed some odd... Changes in the creatures he saw. Some were crying too, and others... Well, others looked like they were going crazy. One of the creatures even attacked Kirby as he was walking. It was odd, because the creatures in this forest were normally very peaceful. Kirby refused to swallow the creature, and instead ran away from it. Kirby didn't feel like killing some creature that was normally very gentle.
As Kirby was near the exit of the forest, he saw his friend Waddle Dee. Kirby was overjoyed when he first saw Waddle Dee, but as Kirby approached him, he froze upon seeing the entire picture.
Waddle Dee was holding his spear, the one he had during their adventure with Magolor, and he was gripping it tightly. He had blood splattered on his face and there was a small pile of corpses of some of the forest creatures in front of him. They all seemed to have been killed mercilessly, and in some disturbing ways. Some appeared to just simply have been stabbed to death, others seemed to have been decapitated, and yet others seemed to have had a sharp object forced down their throat; presumably Waddle Dee's spear. Some of the animals were still alive, but were no doubt suffering. Some were still alive, but with their limbs torn off. Others had their eyes cut out and their jaws torn apart, along with many broken bones.
Kirby was scared to breathe for a second, but then softly said, "P-poyo?"
Waddle Dee did nothing for a second, then slowly got up, turned to face Kirby, and lunged straight for him, spear first.
Kirby quickly ran out of the way. "Poyo!"
Waddle Dee ran at Kirby again, who began running away as fast as he could. "What happened to Waddle Dee?" He thought. After he thought he was a safe distance away, he stopped and looked behind him. Waddle Dee either gave up, or lost track of Kirby. Kirby was worried. It wasn't just Whispy and the forest creatures that have changed. Even Waddle Dee has changed!
Suddenly, Kirby thought of something. What if his other friends aren't the same? Now, Kirby was even more worried. He quickly ran to Dedede's castle.
When Kirby arrived at the castle, he was relieved.
King Dedede isn't any different than usual. He wasn't crazy or depressed, which made Kirby very happy. King Dedede was in the kitchen eating a bunch of snacks. Yep, he's still himself.
The King noticed Kirby standing there and he quickly grabbed his food. "No eating my food, Kirby! It's mine!" Kirby tended to sneak up on Dedede and eat his food.
Kirby smiled. "Poyo!" He decided to head home for now. He was trying to figure out what to do about the whole "craziness and depression" thing going on, and he decided that he'd try to figure it out on his way home.