When Demons wake

You are an Oni in this world. Your mision is to guard the future emporer of the new Japan. But he doesn't seem like that. He seems like any other ordinary person. 

The problem is the Oni king wants to take him over to controll the human world. He sends his minions out to posess him. But you can not let this under any circumstance happen. You are one of the strongest Onis in the whole world. You can kill any small Oni with just one hit. But the size of the batallion can be overwelming.