"nagi" can refer to a number of characters, artists, and other things. Check the current list of nagi* tags to see if there is a more specific one that fits what you are trying to tag.

Some of the more popular tags from that list include...

Artists

• nagifur

Characters

• nagi_(nagifur)

Misc

• naginata for the Japanese pole blade weapon.

...but check the complete list if the one you want isn't listed here.