Entropy is the tendency of all matter in the universe to shift into states of lower energy and an important concept in thermodynamics. According to Gunbuster Science Lessons, Topless abilities are somehow related to this concept through the particle known as Powder.
Scientific Explanation Edit
Entropy is a measure of the chaos of a system: the less organized a system is, the more entropy it has. In the universe, all matter has a tendency to move from a state of high energy and low entropy to a state of low energy and high entropy.