I have him at +Nin -Atk. My reasons:

1. I don't want to sacrifice any of his HP, Def or Res. I want him to stay in the field longer.
2. Since his Mystery, Standard attack and Chase both deal Tai and Nin damage, having a +5% on one and a -5% on another will, theoretically, just balance it out right? But if I upgrade his Mood Levels even just let's say, Mood level 6, +25% Nin, that will still give me a 20% damage boost. Not bad plus none of his defensive stats are compromised.

You're overthinking it too much Solomon :P