Fusion reaction is more energetic than fission reaction because

The energy released in a nuclear reaction is determined by the mass defect, which is the difference between the mass of the reactants and the mass of the products. This mass defect is converted into energy according to Einstein's mass-energy equivalence relation, $E = \Delta m c^2$.

In fission, a heavy nucleus splits into two lighter nuclei, whereas in fusion, two light nuclei combine to form a heavier nucleus. The binding energy per nucleon curve shows that the binding energy per nucleon increases significantly when light nuclei fuse to form a medium-mass nucleus, compared to the change when a heavy nucleus undergoes fission.

Consequently, the energy released per unit mass of the fuel (the mass defect per unit mass of the reactants) is significantly higher for fusion reactions than for fission reactions. This makes fusion reactions more energetic per unit mass of the fuel involved.

Answer: The energy released per unit mass of the fuel in fusion reaction is larger than the energy released per unit mass of the fuel in fission reaction.