godan verb (-nu), intransitive verb
Internet slang spelling of 死ぬ. Used in casual online communication, often for humorous or exaggerated effect. The meaning is identical to standard 死ぬ.
See also: 死ぬ
この問題むずすぎて４ぬ。
This problem is so hard I'm gonna die.
推しが尊すぎて４にそう。
My fave is so precious I could die.