This paper investigates a method for detecting a unique higher-order structure formed by the cooperation of RNA and DNA, known as "RNA/DNA complemented binary G-quadruplex (combiG4)," using a fluorescent molecule called "N-methyl mesoporphyrin IX (NMM)." Recently, "combiG4," where RNA and DNA cooperatively form G4 structures rather than RNA alone, has been reported. However, methods for highly selectively detecting this structure have not been well-established. Therefore, the authors focused on NMM, a fluorescent molecule that strongly emits light when bound to G4 structures, and examined whether it shows a similar fluorescent response to combiG4. In their experiments, they formed combiG4 using model RNA and DNA sequences designed to bind complementarily and bring guanine-rich sequences into close proximity, and then measured NMM fluorescence in this state. As a result, they confirmed that NMM fluorescence significantly increased upon combiG4 formation. Furthermore, similar results were obtained for sequences derived from the KRAS gene, HIV, and dengue virus, suggesting that the method is applicable not only to model sequences but also to biologically relevant sequences. This research provides a foundation for analyzing RNA/DNA complex G4 structures and is expected to be applied to future nucleic acid therapeutics and disease diagnostic technologies.