Sylvia Tilly's deceased high school classmate, whose likeness was used by a being from the mycelial network to communicate with her.
May Ahearn first appears in New Eden as a fellow ensign who advises Sylvia Tilly to use a sample of non-baryonic matter, which saves Terralysium from a deadly radiation shower. Tilly later realizes that May was a high school classmate who died five years earlier. In Point of Light, Paul Stamets and Michael Burnham remove a parasite from Tilly that was causing the hallucination.
The parasite returns in An Obol for Charon. Speaking as May, it accuses Discovery of nearly destroying its species' ecosystem by using the mycelial network for spore jumps, and then it pulls Tilly into the network.
In Saints of Imperfection, May wants Tilly's help against a monster ravaging her world. The monster proves to be Hugh Culber, and Burnham convinces May to use the parasite's cocoon to rebuild Culber's body in normal space.