Answer:
Digestive system. It contains chemical energy. The digestive system breaks down food. Food contains chemical energy. To break down the food, the digestive system contains enzymes. Enzymes have kinetic energy to move and break down the food. They are biological catalysts. They transfer to the thermal energy store since in order to break down food at the fastest rate, they need to be at an optimum temperature.
I'm not sure if it's correct, but I'll provide some energy stores to give you inspiration:
Kinetic energy
Chemical energy
Nuclear energy
Gravitational potential energy
Elastic potential energy
Thermal energy