A discussion about the Demon Keys

I have made reference to the ability to summon demons I've captured, but haven't really talked about what they can do.

First of all, to capture a demon, you have to conquer all of the Demon Circles in its area.  This takes a few trips because you're exploring the area and running into all sorts of monsters.  After that, the demon will wait in a stationary area, but it will be enraged.  This means it's a tough boss fight.  After that, you capture its soul and returning to the inn will have the manager turn it into a key for you (probably after some sidequests and/or cutscenes).  That will allow you to equip its Demon Key.

At the beginning, you start with the ability to equip one Demon Key.  Doing so will allow you to summon that demon in battle.  The equipped demons also have a passive buff and certain abilities the main character can use in battle.  The cost for using the abilities isn't MP or gold, but it reduces the amount of time you can keep the demon out.

Demon Keys can only be equipped at the inn or at a Demon Circle that you have conquered.

Of the demons I have:

Comet detects some unusual aspects in the areas, like secret doors.  She also has an ability that helps you run from battle and abilities to increase the drop rate of items.  In battle, she also fires off healing spells.

Mars provides an increase in the damage of physical attacks your characters do.  She can also do attacks on a group of enemies.  In battle, she's the strongest attacker so far.

Chronos prevents any damage your party would take from squares on the dungeon that would inflict it and reduces the amount of damage your party takes from physical attacks.  In battle, she will sometimes block attacks for the party.

My main character is level 10 now, so he received the ability to have two Demon Keys equipped.  That helps a lot because I was being forced to balance out the risk/reward of the passive abilities.  I would need Comet's ability to progress, but I would want the ability to the others to map things out or make combat easier.