Well, it's also clearly Sullivan because he's flashing back to a scene with only Delkira and the attendant present, and he's obviously not Delkira. Plus the horns are identical too.
People enjoy Iruma's wholesomeness but I personally love his serious side. It has the gap awesomeness of the silly shounen protagonist acting serious for once to let you know shit's getting real (Goku, Luffy, Naruto, etc.) but his default personality is just nice and wholesome rather than mentally challenged, so it's extra great.