You can see the six plots here. Below will be a very, very basic over view of the major mechanics I see for the games.
"The Case of the Well Done Butler": A murder mystery with a spirit detective.
This is primarily a system of rock, paper, scissors. Only instead, it is Divine, Human, Demonic. Divine beats Demonic, since that's just how things go. Demonic corrupts Human, and since Humans have free will, they can trump Divine. Whiskey and Logos deal Divine damage, Killian deals Demonic, while Petra deals Human. This very basic set up quickly gets complicated as you try to have the right people draw the right attacks to keep their overall incoming damage down. The final boss fight is also deterministic; after Petra has completed her investigation, she must:
1. Accuse the murderer in a classic Murder She Wrote "Let's all meet in the parlor" scene
2. Prove her accusation using her Logic Golem's Logical Proofs, Key Items and Things I Learned Menus, sort of like a Phoenix Wright cross-examination
3. Defeat the final boss.
And no, I won't tell you who the actual killer is, but yes, it will be one of the people you can accuse.
"The Robot Island of Dr. Invincible": Super heroes try to stop an army of robots created by Dr. Invincible.
Basic Attacks are not heroic! There are no basic attacks! Instead, everything has cooldowns [managed via states that disable skills.] While some skills are on cooldown, they grant you buffs/debuffs. All heroes also get three limit breaks, which cost all 100 Technique Points [the default limit gauge. We'll rename it to Heroic Willpower or something.] All heroes share two.
Heroic Renewal: Instantly remove all negative status effects; restore 100% health and gain Reraise.
Heroic Strike: Deal 100% more damage for the next turn. These let us do things that super heroes routinely do; get back up after a major beating and turn the tide of a fight with a dramatic surge of power. Each one will also get a character specific special limit break that fills their role. It also means that Eir's buffing/healing role can be de-emphasized some to make her more of a battle maiden and less of a priestess.
"Under the Bed and In the Closet": A widower and a young girl's teacher combine forces to dive into her nightmares.
We are eliminating Magic Points and replacing it with Nightmare Points. Everything you do builds NPs or spends NP. As you fill up NP, enemies do more damage to you. If you reach 100% NP, the character dies and needs to be revived. This represents giving in to despair and the nightmare. In addition, instead of a limit bar, characters start every fight with 100 REM. As they fight in the dream, they risk waking up, "killing" their avatar and needing to be revived. Things can attack you by dealing raw HP damage, increasing your Nightmare value or chipping away at your REM. You can spend REM or NP to do things, but once you spend REM in a fight, it does not come back [except when you're revived.]
"The Castle That Wasn't There": An inquisitor and an unexpected group of allies investigate a mysterious castle.
This will be the most "traditional" RPG. You'll have MP, except for the dwarf fighter, and build up the basic limit gauge. The strength of this is that the turn-based structure is familiar and easy to do. There won't be any mechanical innovations here, instead focusing on the story and atmosphere. The world of the Black Swamp is filled with ghosts and each character has their own reason for delving into the mysteries, leaving the player with a crucial choice for each character to determine their fate after the final boss.
"First and Recursive Contact": When first contact turns out to be with dangerous aliens, a time machine is the only way to prevent humanity's extinction.
A fairly standard RPG with a sci-fi theme, the major mechanic will be playing with variables, specifically Time Locking states, HP, MP, etc. This I'm the least sure that I can make work the way I want, and it probably will be clunky. Instead of MP, we're going to have BP, for Battery Power. The limit/Technique Points remain unchanged.
"The Dame, the Debt and the Devil": A noir where a private eye gets more than he bargained for.
Instead of having hundreds of HP, characters will have very, very low HP. This is a gritty, noir world. You get two resource: Tension Points and they can then Release tension to do something dramatic. Characters build Tension like Limit breaks, but are able to release tension to do things. So, the tank can release tension to put a guard up, which lets him tackle someone out of the way of a dangerous attack. Ideally, the goal in this will be more about avoiding/minimizing damage and less about healing up continually to get the feeling of a gritty fist fight or short range blast out.