It is quasi-Japanese.
"Waifu" is how Japanese pronounce the English word "wife"
It is written in katakana as 「ワイフ」.
Other words are written and said a similar way.
Example: life is 「ライフ」 - "raifu".
President Trump's name is 「 トランプ」 - "Toranpu".
トランプ also refers to western style playing cards.
Daughterfu and gunfu are not katakana. "Daughter" would be written 「 ドーター」 - "dootaa". "Gun" would be written 「 グン」, it is pronounced the same way as the English word.
