  In this paper, we study a tensor product of perfect Kirillov-Reshetikhin
crystals (KR crystals for short) whose levels are not necessarily equal. We
show that, by tensoring with a certain highest weight element, such a crystal
becomes isomorphic as a full subgraph to a certain disjoint union of Demazure
crystals contained in a tensor product of highest weight crystals. Moreover, we
show that this isomorphism preserves their gradings, where the grading on the
tensor product of KR crystals is given by the energy function, and that on the
other side is given by the minus of the action of the degree operator.
