You'll encounter tons of Devil Gates throughout Nippon. They are harder versions of the demons found in the Demon Scrolls, but the same strategies will apply to them. Simply take care of yourself and dodge what you can while dealing damage to the enemies.
Most Devil Gates end up hiding anything from treasure, animals, clovers, or just scenery. There are three in particular that you "will" have to defeat if you want the Stray Beads or the trophy associated with them: