Ever since obtaining the Phantom Ruby, kirbo has always had an increased feeling of negativity towards life, death, basically everything. When fighting the Dark King, Wolfen tells kirbo he's off the team for a bit, as a safeguard due to losing the Phantom Ruby. kirbo takes offense to this, and little known to him, his "impurities" completely took over. Now, he's using all of his skills against Wolfen, or anyone who is even near him.
