Thank you, that's exactly what I was going for! Right now each hero's personality is set when you summon them (Loyal, Cautious, Proud, Vengeful...), and your choices shape their mood rather than their personality. Each personality reacts differently: a Cautious hero is happy when you retreat with plenty of HP, a Proud one gets upset if you retreat too early, a Vengeful one has a nemesis to defeat, and missions that fit their personality make them happier.
But I love your idea of personalities slowly changing with your choices, like a hero becoming Cautious after many careful retreats. I've added it to my list of ideas!