Nowadays, many aromaticity descriptors have been recommended on the basis of multiple manifestations of molecular aromaticity, including geometrical, energetic, electronic, and magnetic ones. However, no single metric can be used independently to reliably measure the aromaticity of a particular system, especially for those with unusual electronic structure. So in most cases, one should examine several aromaticity criteria simultaneously and check if the indices reach the same conclusion or correlate well with each other. Just recently, a comprehensive theoretical study of the aromaticity of the cyclo [18]carbon (C18) and its isoelectronic species was completed by us. The combination of multiple aromaticity metrics suggests that, although B6C6N6 and B9N9 are both isoelectronic analogues of C18, B6C6N6 has a prominent aromaticity comparable to C18, whereas B9N9 is a non-aromatic species. Insightful electronic structure analyses indicate that the aromaticity difference between B6C6N6 and B9N9 arises from the bridging effect of C atoms on the π conjugated path in the former system.