Obviously Imperial Oni is lying sack of shit, but I'm honestly finding myself disliking Mikoto more and more as well. The fact that he's so gullible that he doesn't even consider that Imperial Oni is lying about the Oni he was sent to kill is bad enough, but when said Oni display noble behaviour and outright say they wish for coexistence he really ought to pay attention. At this point he's just a savage thug with very little that separates him from the Oni he hates.
Also, thank fucking God Roam Oni didn't die, that would have been such a waste of a fun character.