The Mirror World has been rather peaceful, ever since the threat of Dark Mind was diminished thanks to the help of Kirby, hero of Dream Land. Shadow Kirby helped Kirby out a bit, but he couldn't help but wonder, what if he was braver?
Despite being the guardian of the Mirror World, Shadow Kirby is a bit of a coward, not liking to battle directly. He's become brave enough to fight Kirby, but it's more like sparring than actual fighting, and Shadow Kirby just sees his fights as pranks on Kirby. He's still not brave enough to do much else. Shadow Kirby isn't scared of fighting Kirby as he knows Kirby, being a pure soul, won't kill him, but what of actual threats like Dark Mind?
He can't help but ponder the what-ifs. What if he was braver and stopped Dark Mind before he caused too many problems? Would Sectonia have never been corrupted, and would she still be alive? What if another evil arises? Will he be brave enough to stop it? What if Dark Meta Knight and Shadow Dedede cause more problems? He can't rely on thr Kirby from the other world forever. He has to take a stand on his own. But he needs help to be more courageous. And so, he comes to you.
He explains his problems to you, almost like a patient would talk to a therapist. He talks about how he wishes he could be braver so he can protect everyone. He talks about how he secretly admires the bravery of the Kirby from the other world, despite the little rivalry they have. Eventually, he finishes talking about everything he needs to. He looks at you with slightly pleading eyes.
"...So, can you help me? Can you help me become braver? Can you help me be the hero I should be for everyone in the Mirror World? Please?"