In the anime adaptation of the manga The Quintessential Quintuplets, as well as the corresponding manga, I notice there are 2 times 'obake' was used. I finished the anime s1 and s2, but I'm just now reading the manga, and I notice there's a difference in obake used in 2 scenes - 1 is with hiragana and 1 is with katakana.
Scene 1: S01E01
Re 2 of the quintuplets Nino (who is older, if relevant) and female protagonist Itsuki: Nino says to (or about) Itsuki 'この肉まんおばけ.' (You can see 0:06 - 0:10 here.)
Scene 2: S01E08
Re the siblings Fuutarou and Raiha, Raiha (who is younger, if relevant) asks their dad if Fuutarou, the male protagonist, was not always a...
Anime Subtitles: ... a 'study freak'.
Manga English: ... a 'study monster'.
In the anime and manga original, Raiha asks '前はこんな勉強オバケじゃなかったの?' (You can see 1:57 - 2:02 here.)
I was curious but never really bothered to look up the exact furigana/hiragana/katakana or whatever of what Raiha said which sounded like 'benkyou baka (ばか)' (like...study idiot?). But when I saw 'study monster' in the manga. I got really curious and then saw - ok the Japanese word for 'monster' here is indeed the same as 'monster' for Itsuki. So it was actually 'benkyou o(something)' and then 'bake' instead of 'baka'.
Now comparing both:
So it appears both protagonists here are described by their siblings as monsters...but the difference is the katakana vs hiragana:
Katakana オバケ - is used by Raiha for Fuutarou.
Hiragana おばけ - is used by Nino for Itsuki.
Based on the above linked questions, I guess it's to do with bold/italics or something. But then...I'd think it would be the reverse. At least in the anime, Nino says obake with emphasis while Raiha doesn't. It's like
- For Nino: (You can see 0:06 - 0:10 here that there is emphasis on 'obake'.)
Nino says: kono nikuman OBAKE!!!
- For Raiha: (You can see 1:57 - 2:02 here. I really don't think there's an emphasis on 'obake here.)
Raiha says: Mae wa kon'na benkyō obake janakatta no? (That's it. There's no bold/italics on the 'obake' here.)