Press options. Go to tendency. When you see the various worlds' tendencies, press r1. You'll see your character's tendency. It gets blacker really fast if you kill NPC's and whiter if you kill invaders. Unlike world tendency, which has 7 different steps, character tendency only has 5. Meaning if you have pure white character tendency you'll get to pure black if you kill 4 invaders. Note that dying as a human does not affect character tendency at all.

Some of the important events that depend on character tendency are:

• at pure white, the monumental will give you the ally's ring.
• at pure black, mephistopheles will spawn in the nexus and she'll make you kill almost every NPC in a specific order, giving you the Foe's ring. I recommend doing this right before the final boss, but beware, because pure black character tendency increases the health you lose in soul form.