Hereward is the third-tier Persona of Goro Akechi. His Trait is Ingenious Spirit, which may decrease the SP cost of allies' support/Almighty skills by half.
In order for Loki to evolve into Hereward, the protagonist must do the following:
During rank 7 of Akechi's Confidant, pick "You're my rival"
During rank 8 of Akechi's Confidant, accept his glove
In a new scene attained during the night after defeating Akechi in Shido's Palace, remember your promise to him
Hereward learns a unique skill upon its evolution from Loki, Rebellion Blade (反逆の刄, Hangyaku no Ha)?, which deals colossal 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 him or view his entry in the compendium prior to February 3rd, where combat is last available. This applies even for New Game Plus.
In a 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. It also can be seen as a visual combination of Robin Hood and Loki, incorporating the bow and weapon of the former and the Dark aesthetics of the latter.
Hereward is one of only two 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.
Hereward's Awakening is the only third tier Persona awakening that is fully voiced.