What is the difference between Okaa-san/Onee-san/Ojii-san and Kaa-san/Nee-san/Jii-san


i was playing Katahane last night, in it Light and Wakaba refer to their
mother as Kaa-san while Light refers to Wakaba (his older sister) as Nee-san
and when meeting with Rien he says for them to call him Jii-san by commenting

> If you did not know my name or who i was i would just be an old man to you
> correct?

^ (he's not saying that in a bad way mind you)

also in Fate/Stay Night, Sakura refers to Rin as Nee-san and the 2 of them are
sister however Sakura was adopted out to prevent a potential fight over Magus
Succession between them (like what happens with Touko and Aoko)

from my understanding, Okaa-san is Mother, Onee-San is Big Sister and Ojii-san
is Grandfather, now while Kaa-san and Nee-san i can still determine refer to
Mother and Sister i'm assuming Jii-san is something close to Grandfather as
Rein in Katahane is almost like a grandfather to Cero and since Wakaba is
close to Cero (potential love interest in one route) i'm assuming he doesn't
mind being though of as a grandfather but that's seculation,

so i am wondering, what is the difference between Okaa-san/Onee-san/Ojii-san
and Kaa-san/Nee-san/Jii-san apart from the obvious drop of O from each word




お _o_ is an "honorific prefix" (read about [honorific speech in
Japanese](http://en.wikipedia.org/wiki/Honorific_speech_in_Japanese#Honorific_prefixes)
on Wikipedia), which is a more polite way to refer to someone's or your own
grandfather/mother/sister/etc.

There is also お父さん _otōsan_ "father", おばあさん _obāsan_ "grandmother" and お兄さん
_oniisan_ "big brother", which fit the same pattern.

We have a few questions about お and its "brother" ご [on this
site](https://japanese.stackexchange.com/search?q=%E3%81%8A+%E3%81%94), which
might be of interest. You'll probably understand the meaning of お from reading
these questions alone.




お _o_ is an "honorific prefix" (read about [honorific speech in
Japanese](http://en.wikipedia.org/wiki/Honorific_speech_in_Japanese#Honorific_prefixes)
on Wikipedia), which is a more polite way to refer to someone's or your own
grandfather/mother/sister/etc.

There is also お父さん _otōsan_ "father", おばあさん _obāsan_ "grandmother" and お兄さん
_oniisan_ "big brother", which fit the same pattern.

We have a few questions about お and its "brother" ご [on this
site](https://japanese.stackexchange.com/search?q=%E3%81%8A+%E3%81%94), which
might be of interest. You'll probably understand the meaning of お from reading
these questions alone.

