Tales of Phantasia

Make sure you have the proper Pact Ring, im not sure which, check a FAQ.

Look for the lapis pact ring which is somewhere in the dwarven temple in a fake wall

just use Chester and use his skill gale shot to Pluto
try it its use full ^^

just don't step to close to Pluto(attk 999)
and Cress or Cless is useless against him
he can't come close because pluto is protected by a circle of flames
use your mages, healer and archer
set them to max tp consumption as strategy and prevent pluto from casting spells with Chester as long as your mages need to take him out

Keep using demon fang I would say.

You can also use spells and chesters arrow skills, except sonic bash because when he uses it he kind of gets near pluto a little too much