In a medium skillet, add the olive oil over medium heat and wait for it to be hot. Cut the base of the shimeji (that binds them all together), separate each one, and add them to the skillet. Sauté the mushrooms until they start to get some golden spots.
Add soy sauce and rice vinegar, and cook for about 3 more minutes. Push them all to one side of the pan and add the butter and garlic to the other side. Sauté the garlic until fragrant, and then stir everything together. Cook for one more minute or until the shimeji reaches the desired color and consistency.
Transfer the mushrooms to a serving dish and sprinkle with chives.Serve it while still hot.