Looking at the interaction in between the Hero and Ougi in ch.20... The implication of the 4 headless figures lining up (page 17, ch.7) during the dream sequence Ougi had, where the Hero was shown dining on his (Ougi's) head is much clearer now.
I had a quick reread of ch.1 and caught something which I didn't notice before: the entity which asked Ougi if he wanted to live while he was dying from the stab wound is very much the Hero himself. The collar of the entity's coat (page 12, ch.1) is identical to that of what Ougi is wearing (first seen page 35, ch.1).
While the Hero seemed to be protecting Ougi's consciousness during the fight against Portia's mutated form, earlier chapters are also implying that the Hero's actively consuming Ougi as shown by the head consumption scene and following it up with Ougi forgetting some things about himself. The reason and future implications for this is unknown right now, and is the main attraction for me towards this manga.