Nu (ぬ) is an auxiliary verb suffix
that turns a verb into a negative verb. It's similar to the -nai
suffix that most beginning Japanese students learn, but it's much older and more rarely used.
-Nu is appended to the same base as -nai, but conjugates differently. In the renyokei form (-naku), it becomes -zu. In the conditional form (-nakere), it becomes -ne.
If that made no sense at all to you, here are some examples on how -nu is used:
Dôshite mo ikaneba naranu (= Dôshite mo ikanakereba naranai).
I have to go no matter what.
Ikenu mono wa dô shiyô ka? (= Ikenai mono wa dô shiyô ka?)
What shall we do about those who cannot go?
Shirazu aruite kita (= Shiranaku aruite kita).
In spite of myself, I walked over.
The final -n in polite -masen
verbs is actually a contraction of -nu.