harshness vs unpleasantness

harshness and unpleasantness both are nouns.

Word	Noun	Adjective	Verb	Adverb
harshness	Yes	No	No	No
unpleasantness	Yes	No	No	No

As nouns, unpleasantness is a hypernym of harshness; that is, unpleasantness is a word with a broader meaning than harshness:

harshness (noun)	unpleasantness (noun)
the quality of being harsh or rough or grating to the senses	the quality of giving displeasure
excessive sternness	the feeling caused by disagreeable stimuli; one pole of a continuum of states of feeling
the roughness of a substance that causes abrasions
the quality of being cruel and causing tension or annoyance