Raising Dororo's HP
As you play the game, notice that Dororo gets a heart
after killing a demon. The heart increases his maximum HP. In
Chapter 4, when you play as him for the first time, you will encounter
three portals that put out wolves. Destroy two of the portals
and focus on the wolves that are exiting from the last one. Every
two or three that are killed will drop a heart. Make sure not
to destroy the portal until you have all the health that you desire.
Quick sword level up
Find a location that only as a portal that lets out
birds with nothing else around to interrupt you. As soon as the
birds appear, kill them with you arm swords, but make sure that
you do not hit the portal or it will be destroyed after a few
hits. The left arm levels up more quickly than the right arm.
However, with some time you can get them leveled to a decent level
at the start of the game to help you in the Boss fights that happen
later.