  We systemically study the Hecke relations and the $c=8k$ coset relations
among 2d rational conformal field theories (RCFTs) with up to seven characters.
We propose that the characters of any 2d RCFT -- unitary or non-unitary --
satisfying a holomorphic modular linear differential equation (MLDE) can be
realized as either a Hecke image or the coset of a Hecke image with respect to
a $c=8k$ theory. Benefited from the recent results on holomorphic modular
bootstrap, we check this proposal for all admissible theories with up to five
characters. We also find many new interesting Hecke relations. For example, the
characters of WZW models $(E_{6})_2,(E_7)_2,(E_{7\frac12})_2$ can be realized
as the Hecke images $\mathsf{T}_{13},\mathsf{T}_{19},\mathsf{T}_{19}$ of
Virasoro minimal models $M_{\rm sub}(7,6),M(5,4),M_{\rm eff}(13,2)$
respectively. Besides, we find the characters associated to the second largest
Fisher group $Fi_{23}$ and the Harada-Norton group $HN$ can be realized as the
Hecke images $\mathsf{T}_{23},\mathsf{T}_{19}$ of the product theories $M_{\rm
eff}(5,2)\otimes M_{\rm eff}(7,2)$ and $M_{\rm eff}(7,2)^{\otimes 2}$
respectively. Mathematically, our study provides a great many interesting
examples of vector-valued modular functions up to rank seven.
