Rannus was a member of the Shadow Kin and loyally served his King Corakinus.
When Corakinus began sharing schoolgirl April MacLean's heart in order to stay alive, after his own was displaced due to being shot by Andrea Quill's displacement gun, (TV: For Tonight We Might Die) Rannus was enlisted to find a way to break the connection between Corakinus and April. Rannus came up with the idea of using an "anchor of a life blood" that would be attached to the heart to force it to stay in Corakinus' body rather than swap between his and April's. This failed and an enraged Corakinus executed Rannus.
Later, Kharrus, Corakinus' next consultant, commented that Rannus had been too cowardly to go the extra step and attach Corakinus' whole body to the anchor. (TV: Co-Owner of a Lonely Heart)