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The extremely luminous comma fast comma hot transient AT2018cow has provoked a reconsideration in our view of the transient sky. This event comma by far the nearest example of the class of fast-rising luminous transients (sometimes referred to as FBOTs or FELTs) comma displayed an array of peculiar properties that highly strain theoretical models for what is possible in a supernova explosion. For all their peculiarities comma however comma fast-rising transients are not rare in a volumetric sense - and with ZTF and ATLAS both obtaining high-cadence observations of wide areas of the northern sky it is probable that another such event will be observed in the coming year. These are primarily ultraviolet phenomena comma and UV spectroscopy has the power to reveal similarities or differences betwen this event and other known varieties of transient (including young CCSNe comma superluminous SNe comma and TDEs) that are not apparent in optical observations alone comma and to discover (or rule out) the presence of a dense stellar wind around the progenitor. We propose to obtain target-of-opportunity UV spectroscopy of another event of this type in Cycle 28 to critically evaluate these links and secure the physical origins of this class while HST.s unique UV spectroscopic resource is still available.