Following the discovery, observations of SN 2017dio show that it is best characterised by a type-Ic classification, but with emission lines of H and He superimposed on the spectrum. These lines are always present in the spectra since the early stage, and thought to originate from the interaction between the supernova ejecta and a nearby circumstellar medium (CSM). As such, SN 2017dio exemplifies the first example of a SN Ic with prompt H-rich CSM interaction. The CSM is unlikely to have been produced by steady stellar winds of the progenitor, and requires intense mass loss in the order of 0.02 Msun/yr. Progenitor eruptions, or interactions with a close binary companion, may have caused the high mass loss rate and the CSM concentration in the immediate vicinity of the stripped progenitor star.