Onii-chan or nii-san?

Question

I write a lot of fanfiction on Japanese anime and I need to get this one thing straight: What's the difference between nii-san, onii-san, nii-chan, and onii-chan? I hear all of them interchangeably.

And what ending do you use for "outoto"?

Answer 1

O is used in Japanese to be honourable. Chan is for young boys I think? San is for anyone.

Now answer mine:

http://answers.yahoo.com/question/index;...

Answer 2

It's just politeness... From polite to informal (that I can think of right now)...

Onii-sama, nii-sama, onii-san, nii-san, onii-chan, nii-chan...

Otouto doesn't need any ending because they are younger.

Edit: Younger kids get less respect, that's why otouto gets no ending... Normally they would just be called by their name and maybe -chan at the end.