A functor $F\colon \mathcal{C}\to \mathcal{D}$ is corepresentably faithful on cores if, for each $X\in \operatorname {\mathrm{Obj}}\webleft (\mathsf{Cats}\webright )$, the postcomposition by $F$ functor
is faithful.
Let $\mathcal{C}$ and $\mathcal{D}$ be categories.
A functor $F\colon \mathcal{C}\to \mathcal{D}$ is corepresentably faithful on cores if, for each $X\in \operatorname {\mathrm{Obj}}\webleft (\mathsf{Cats}\webright )$, the postcomposition by $F$ functor
is faithful.
In detail, a functor $F\colon \mathcal{C}\to \mathcal{D}$ is corepresentably faithful on cores if, given a diagram of the form
then $\alpha =\beta $.
Is there a characterisation of functors corepresentably faithful on cores?