At least the beast tamer is not a girl failure. Yeah thinking it is time to go full 40s drill sgt. Either they Gomer Pyle you or the shape up. Either way you will have fine marines
Let me guess the Demon King is the same useless shit like her (it's 100% female in this manga genre) 3 subordinates. The only solution is being heartless and leave the castle alone. Leave them to fend off by themselves.
Just like Ivan Drago said: "if they die, they die."