Hereward is the third-tier Persona of Goro Akechi. In order for Loki to evolve into Hereward, first, after defeating Akechi in Shido's Palace, the protagonist must choose to fulfill his promise with him. Then on the 2nd of Feburary, after sending Takuto Maruki the calling card and being asked by Akechi about the false reality, he must then not accept it; Accepting it results in a bad ending. Once he does, Loki and Robin Hood merge to become Hereward.
It learns a unique skill upon its evolution from Loki, Rebel's Blade (反逆の刄, Hangyaku no Ha)?, which deals severe Almighty damage to a single target and deals bonus damage to enemies that are knocked down.
Due to the unique unlocking conditions of this Persona, it is impossible to use it or view its entry in the compendium prior to February 3rd, where combat is last available. This applies even for New Game Plus.
Concept art of Hereward, as seen in the Thieves Den gallery
In similar vein to how Robin Hood's design was largely inspired by comic book hero Superman, Hereward's design may have been inspired by Batman, hence the black armor and the bat wing-like protrusions on the back of his head. This may be an allusion to Akechi's role in the third semester, symbolizing his transformation from a seemingly-altruistic hero to a feared warrior seeking to see through his own personal justice.
Hereward is one of the only 2 third tier Personas that can be unlocked during the story. The other Persona is Morgana's Diego.
Hereward is unique among third tier Personas in Royal, as he is not fused through the combination of the first and second tier forms of a single Persona, but rather from two standalone Personas; Loki and Robin Hood.