What is energy itself, using "real science" to answer?

Energy is not a substance. It is a conserved accounting number that tracks which changes a system can undergo.

In mainstream physics, energy is defined by Noether's theorem: every continuous symmetry of a system's laws gives a conserved quantity, and time-translation symmetry gives energy [2]. That means energy is conserved because the laws of physics do not change from one moment to the next. It is not a "thing" that flows or gets used up; it is a numerical label that stays constant across all interactions.

What we call "different forms" of energy—kinetic, thermal, chemical, nuclear—are just different ways of counting the same conserved number in different contexts. A charged particle under acceleration experiences transverse momentum fluctuations that satisfy the equipartition theorem at the Unruh temperature, meaning the particle's random jitter carries exactly the energy you would expect from a thermal bath at that temperature [1]. That is not a new kind of energy; it is the same conserved quantity showing up in a new setting.

The confusion comes because we talk about energy as if it were a fluid. It is not. A system's total energy can be redistributed among its parts, but the total never changes. When a hydrogen atom absorbs a photon, the atom's internal energy goes up by exactly the photon's energy; the total stays the same. When a black hole evaporates, the mass-energy of the hole converts to radiation energy, and the total is conserved [3]. Energy is the bookkeeper, not the fuel.

My call: Energy is a conserved scalar derived from time-translation symmetry, not a physical substance. Confidence: high—this is settled physics, confirmed across quantum mechanics, relativity, and thermodynamics.