I can't remember the equipment details of how I got thru this, but what I would suggest is to make sure that you have the best possible equipment and enough items during the fight. The rat stew increases your virility (damage you make to the enemy), so maybe use it early into the fight. Also, don't forget to find their weakness to deal the highest damage.
The pear will be available once you open up Feasterra, which I think comes after you've rescued the 3 villagers, so don't worry about the underwear yet. You'll get to it eventually.