The Ninja quest bug
:
1. Enter the ruins, do what you want (including killing the ghosts).
2. Lower the drawbridge.
3. Return to the town and get the Ninja Quest. You can go to Bushi Dojo immediately and become a ninja - because the bridge is down (you have done it already) and no ghosts have seen you after getting the quest (sure, they are in the ruins and you are in the town).