I only noticed it after re-reading it, but page 11(?) of chapter 4, in the second to last panel made a joke reference (hero's coffin joining a monster?) to the monster taming system where defeated monsters can be picked up as part members.
hmmm. I'm not sure its referencing that system, I read it as another joke about the goblin encouraging aki to stop crying so much about being murdered, cuz the coffins actually love aki and just want to be her friend.
no the joke was directly a jab at how monsters want to join your party in Dragon Quest. The text is basically the same and the series is already full of dragon quest references.