Using a “QMS” (Quadrupole Mass Spectrometer), the authors detected a significantly large amount (10²⁰-10²¹ [cm^-3]) of helium (⁴₂He), which was concluded to have been produced by a deuterium nuclear reaction within a host solid. These results were found to be fully repeatable and supported the authors' proposition1) that solid state plasma fusion (“Cold Fusion”) can be generated in energetic deuterium Strongly Coupled Plasma (“SC-plasma”). This fusion reaction is thought to be sustained by localized “Latticequake” in a solid-state media with the deuterium density equivalent to that of the host solid. While exploring this basic proposition, the characteristic differences when compared with ultra high temperature-state plasma fusion (“Hot Fusion”) are clarified. In general, the most essential reaction product in both types of the deuterium plasma fusion is considered to be helium, irrespective of the “well-known and/or unknown reactions”, which is stored within the solid-state medium in abundance as a “Residual Product”, but which generally can not enter into nor be released from host-solid at a room temperature. Even measuring instruments with relatively poor sensitivity should be able to easily detect such residual helium. An absence of residual helium means that no nuclear fusion reaction has occurred, whereas its presence provides crucial evidence that nuclear fusion has, in fact, occurred in the solid.