Dahlia is a recurring supporting character in TJA Projects and, arguably, the series' most important character. The toddler daughter of TJ and Jake is first seen in My Baby is Home and last seen in Breaking Point, although she is mentioned in later entries.
In the original Slender Man creepypasta, the entity typically haunts or is associated with young children. As such, almost immediately with Dahlia's introduction came the theory that the goal of the Slender Man and his minions was to abduct or otherwise harm the child. Much of the narrative tension of the TJA Projects series involves TJ and Amy's attempts both to solve the mystery of the Slender Man and to protect Dahlia from the supernatural forces surrounding her.