I am huge fan of the series and I like the dynamics between the characters. I would have loved something quick and small to play and I thought a card game could work well. While meditating on the mechanics, it rapidly ended up as a trick taking game.
It might end up a bit more abstract than expected, but I might get a working game faster this way.
Here is how it goes. It's basically only a 5 player game, (maybe some adjustments can be made for varying amount of players, like restricted characters, bonus nb of cards, etc).
Each round is a mission. Mission are on a cards, it gives a special rule for this round and has a list the required tricks to succeed. For example, you need to win 4 spades, 3 hearts and 2 clubs tricks to succeed.
I am not sure if I am going to use a 4 or 5 suite deck. When you win a trick, the leading suit card is placed on the top of the trick when collected. Cards with low values will have special abilities than can be used only by lupin (Gadgets, tricks, etc) or by Zenginata (Defenses, assets).
Now what makes the game unique is the dynamics of the characters.
Goemon: Ignore suites, only values matter.
Jigen: Card values get a bonus or are doubled.
Lupin: Can use the trick/gadget special abilities on cards
Zenginata: Can use the Defenses special abilities on cards
Fujiko: Can get a gift card from lupin's hand which he then replaces from the top of the deck.
In order to win, the "Thieves" gang need to win the tricks above. Or if the gang wins but Fujiko has more than X trick of any suite (determined by the mission), she wins. If the Thieves gang fails, Zenginata wins.
Players collect points according to the mission and winning teams. There could be a special ability cards that allows lupin and zenginata to switch place during play.
What do you think?
I have refined my ideas a bit and it now looks more interesting.
Mission would only have a special rule and a trump suite which can be anything but hearts. Special rules could be something like "don't play 2 consecutive numbers in the same trick"
At the beginning of the game, all players except lupin give a heart card to fujiko and she give back a card to each player.
Then Goemon and Jigen give 2 cards to lupin each. This is used as A) for communication on their hand, and B) to give special ability cards to lupin. Lupin will give 2 cards back to each of those players once the plan is chosen.
Then lupin chose a plan. Plan cards has the list of suites required to win. He chose a plan card out of 3 and show it only to goemon on jigen, but not to fujiko and zenginata. Fujiko's won trick still count for victory, but she does not know what is required. She only need a fixed amount of tricks to win (maybe even if the thief gang fails)
The character abilities are now slightly different
Goemon: ignore suits, use only value
Jigen: is the Only player to be able to use the trump suite
Lupin: is the Only player to be able to use the special abilities on low cards.
Fujiko: She may give a heart card to lupin before playing her card to get a "gift" card from lupin.
Zenginata: I am not sure about his ability. It should be related to either deduction or Observations. Idea A) The special rule on the mission card is enforced by zenginata only, so player can try to cheat that rule, if zenginata fail to notice it, it passes. Idea B) The 2 joker cards are lupin cards. They can be discarded by players maybe if they cannot follow suite. Zenginata needs to catch the trick containing those cards. Doing so will "destroy" a won trick of his choice at the end of the game (before looking at the plan objective). At the end of the round, any lupin cards not played goes to zenginata.
There will not be place switching during the game, but if the player want to change character between rounds, they can. In that case, they need to keep track of their score individually.
I am not sure if the players must be placed in a specific order to play cards. Maybe certain order of players could be too weak or too strong.
As for varying nb of players I was thinking to use:
3P: Lupin, Jigen, Zenginata 4P: Lupin, Jigen, Fujiko, Zenginata
Maybe a ghost hand with excess cards will be placed in the middle of the board allowing players to exchange cards in a certain way at the beginning of the mission. This will be the only way to balance nb of players.