So I've noticed that the more skills on a unit, the more new skills cost when you pay to learn them off of einherjar or after castle battles. Another reason why the Gold map dlc is actually worth buying, even if you don't get the full dlc bundle.
And the Bond unit feature is actually pretty neat. If you keep giving accessories to the same people, eventually your 'bond' with them grows deep and creates a new unit.
It creates a new unit that's like a young avatar, it comes with one 'personal' ability and 3 others. I think the class is based off the other person's heart seal class, and takes one or two abilities from your avatar and theirs that appear at the bottom of the ability list, as I guess it assumes that to be the most recent ones learned. Hair color seems 50/50 either their avatar's or yours.
Now I want to make an army of bond unit minions.