The nature of chemical bonds is of fundamental importance in chemistry. Clarifying the new facets of covalent bonds is also helpful to promote green chemistry by allowing chemists to design novel chemical products and new processes to advance sustainability. We have successfully synthesized highly strained “core-shell”-type hydrocarbons and demonstrated that the C–C covalent bond can be expanded beyond 1.80 Å, which is 1.17 times greater than the standard length (1.54 Å). By the discovery of such a “hyper covalent bond,” the covalently bonded state and non-bonded state are seamlessly connected in terms of the interatomic distance. Compounds with the hyper covalent bond are potential candidates for making a novel class of materials whose crystals, films, or polymers can respond to external mechanical stimuli with anisotropic contraction or expansion of the matter, accompanied by reversible compression, extension, or fission of the “bond” in the molecule.