Sauté the pork on medium-high heat until browned. Add the chopped kimchi, reserving the kimchi liquid, and stir regularly until kimchi is heated fully. Add the water and broth. Add the soy sauce, mirin, gochujang, and kimchi liquid. Stir and cook until the stew starts to simmer. Stir in the shredded garlic. Add the mushroom and the green onions, stirring to mix. Lay the tofu across the top of the stew, spooning some of the stew over the tofu to coat. Cover the soup and cook for 5-10 minutes or until the mushrooms and tofu are cooked through. Spoon the stew into bowls and drop about 1 tsp of butter on the top of each bowl. Serve with a side bowl of cooked white rice.