I'm trying to see if I can construct a monoidal category $\mathbf{C}$ whose objects are the irreducible unitary highest weight representations of the Virasoro algebra.
I am thinking on doing the following, which seems quite natural: start with the category $\mathbf{Rep}(Vir)$ and let $\mathbf{C}$ the full subcategory whose objects are the irreducible unitary highest weight representations.
But now if we take the tensor product to be the usual tensor product of representations of a Lie algebra, then the tensor product of two objects of $\mathbf{C}$ may be reducible in general, and thus the category is not monoidal. (This is my only issue, since the tensor product of arrows will be trivially in $\mathbf{C}$ because this subcategory is full, and also $\mathbf{1}$ (the unit of the monoidal category $\mathbf{Rep}(Vir)$) is in $\mathbf C$).
Is there a way to fix this problem?