1. ogre; demon; oni
だから私も、鬼を倒しに行きます。So I am also going to defeat the oni.
2. spirit of a deceased person
3. ogre-like person (i.e. fierce, relentless, merciless, etc.)
when read as "おに"
鬼か、あんたは！What are you, some kind of monster?!
4. it (in a game of tag, hide-and-seek, etc.); seeker; chaser; tagger; tigger
when read as "おに"
まず、鬼を決めよう。First, let's decide who's it.
5. Chinese "ghost" constellation (one of the 28 mansions)
when read as "き"
6. very; extremely; super-
when read as "おに"
この問題、鬼難しいんだけど。This problem is insanely hard.