waifu vs fictitious character

waifu and fictitious character both are nouns.

Word	Noun	Adjective	Verb	Adverb
waifu	Yes	No	No	No
fictitious character	Yes	No	No	No

As nouns, fictitious character is a hypernym of waifu; that is, fictitious character is a word with a broader meaning than waifu:

waifu: a character in an anime or manga who one has romantic feelings for
fictitious character: an imaginary person represented in a work of fiction (play or film or story)

Other hypernyms of waifu include character, fictional character.

waifu (noun)	fictitious character (noun)
a character in an anime or manga who one has romantic feelings for	an imaginary person represented in a work of fiction (play or film or story)