Clarissa was one of a group of orphaned children taken in by Shannon and Frederick Rivers when they attempted to scavenge for supplies at Riverside Manor. She was a little younger than the Rivers' own child, Olivia. This small group would eventually grow with the influx of more orphaned children under the Rivers' wing and laid the foundation for the development of the Order of Mysteries.
Clarissa was the first casualty of the Order during a surveillance mission on February 7, 2086. Although Olivia had previously felt resentful of all of the orphans her mother had taken in over the years, Clarissa's death profoundly affected her. The incident likewise had a significant impact on the organization as a whole, causing some members to begin to question the goals and ambitions of the group. Olivia was angry and frustrated, quickly becoming bitter and disillusioned at her mother's lackluster response to Clarissa's death.
Clarissa is mentioned only in Fallout 76.