After activating and going into Extreme Heat Mode, you can further activate what is known as a Quick Time Event. In order to make such a thing occur, you will need to land enough punches with Kiryu consecutively on one of your opponents (again, while in Extreme Heat Mode). Quick Time Events a little difficult to complete, but they can see you dealing incredible damage to an opponent in a very short period of time.
If you having trouble with the complexity of Quick Time Events, there is a trick you can do to make sure use always properly complete them. You see, the Order of the Buttons you will have to press during a Quick Time Event will always go in a specific order. This order is as the following: Square, Triangle, Circle, Square, Triangle, Circle. Since this pattern has a repeating sequence, it is quite easy to remember on the fly. Should you be able to memorize it, you will always get the maximum out of Quick Time Events, which would be the Key to victory in a difficult Boss Battle.