[Serie: All About Japanese Particles]
1. Indicates emotion. Mostly used by men.
Note: Na in this usage is often lengthened to nā.
Ano hito wa subarashii nā.
She’s really great [something]!
Kirei na hoshi da nā.
What a beautiful star!
2. Ask for another person’s agreement. Used by men.
Ano kuruma wa shinsha da yo na.
That’s a new car, right? / That’s a new car, I bet.
Asoko wa samui na.
It’s cold there, isn’t it.
3. Softens the effect of an assertion.
Ano hito wa nakanaka rippa na hito da to omou na.
I really think [I’d say] that he is a fine, upstanding person.
Kono eiga wa yoku nakatta na.
This movie just wasn’t very good.
4. Softens a command or request (first example, a woman speaking with typical kudasai na pattern; second example, a man).
Narita made itte kudasai na.
Narita [Airport], please [if you please].
Ashita kanarazu koi na.
Be sure to come tomorrow.
5. Indicates a prohibition. Used by men.
Zettai ni aitsu ni au na.
Stay away from that bum, you hear./ Keep clear of that guy.
Mō ano bā ni iku na.
Don’t go to that bar ever again!/ No more going to that bar, hear.
– Source: All about particles – A handbook of Japanese function words –