Only on Level 7
Story related and cannot be missed.
Once the ghosts appear in the graveyard, take the stairs to your right. You will find a gazebo where you can find an Anemone flower. The shrine is behind it (use your Detect Kuji Shrine spell if you're not sure). You will get the Sunrays spell, that you will need to kill ALL the ghosts on the way to the Night Castle.
Once you've killed the last remaining ghost, the achievements pops.
If you're getting low on Ki energy, either backtrack and don't touch the controller for a minute or two (Hiro will start meditating which will restore your Ki faster), or use a Flask of strong ginseng.