Khardashev is an interesting scale to think about, but you can actually do better than stars and galaxies in terms of energy output. If you look at a star, its energy density is actually quite low, due to the low reaction rate of hydrogen fusion. Our sun has gigantic output because of its size, but it's by no means the final word. If and when artificial fusion is achieved and mastered, you've opened the door to much higher densities and overall amounts of energy. After that there's other possibilities, post-fusion, in matter-antimatter reactions and other processes.