states such as diradicals, Jahn-Teller distortion as well as bond-breaking. Furthermore, the one-electron spin-flip excitation from the mixed triplet reference includes the important doubly excited configuration, which is the main ingredient to properly account for the conical intersection CI 21 between bright 1 1 B + u and dark 2 A - g states of s-trans-butadiene and s-trans-hexatriene. Therefore, after its initial introductions, the MRSF-TDDFT has proven to be a promising quantum theory for general use, overcoming the major issues of existing theories. In a series of studies, it has been demonstrated that the MRSF-TDDFT approach can also yield accurate nonadiabatic coupling matrix elements (NACMEs) enabling reliable nonadiabatic molecular dynamics (NAMD) simulations, accurate spin-orbit couplings (SOC) and very accurate X-ray absorption predictions. This method has also been successfully used in designing highly performing optoelectronic materials. The MRSF-TDDFT has finally been released publicly by the GAMESS (July 31, 2022 R1 Public Release Version). As a variant of linear response theory, the performance of MRSF-TDDFT is also subjective to the choice of exchange-correlation (XC) functionals. As was pointed out by Huix-Rotllant et al., within the widely used collinear (one-component) SF formalism, which is also adopted by MRSF-TDDFT, the configurations obtained by different SF transitions couple through the exact exchange only. It inevitably requires a larger fraction of the exact exchange, such as in the BH&HLYP functional, limiting the choice of XC functionals. Therefore, the main objective of the current study is to explore a way of developing customized XC functionals for MRSF-TDDFT as well as linear response theories in general. Vertical excitation energies (VEEs) may be one of the important criteria for this, which are the properties at Franck-Condon (FC) geometries. In the special applications of nonadiabatic molecular dynamics (NAMD), however, various other parts of potential energy surfaces away from FC are frequently encountered. Especially, the conical intersection (CI) regions are of utmost importance for the success of NAMD simulations. However, properly established CIs that can be adopted for benchmarks, are scarce in the literature. In the current study, the two conical intersections of trans-butadiene 12 and thymine shall be adopted.